[Regression] Update icon paths for Signal systray images.

[zquestz]

This PR updates signal.electron.json to swap the signal-desktop systray icons.

Fixes #771

[abouvier]

signal-desktop now uses these files:

images/tray-icons/base/signal-tray-icon-16x16-base.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-1.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-2.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-3.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-4.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-5.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-6.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-7.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-8.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-9.png
images/tray-icons/alert/signal-tray-icon-16x16-alert-9+.png

[zquestz]

@abouvier thanks for the heads-up. I have updated the PR to work with their new image layout, however it seems something is wrong decompressing their app.asar file with the latest release!

I am getting the following errors trying to apply the new icons. That being said, it appears the icon swap still works.

warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/better-sqlite3/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/better-sqlite3/build/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/better-sqlite3/build/Release/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/better-sqlite3/build/Release/better_sqlite3.node
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/libsignal-client/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/libsignal-client/prebuilds/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/libsignal-client/prebuilds/linux-x64/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/libsignal-client/prebuilds/linux-x64/@signalapp+libsignal-client.node
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/ringrtc/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/ringrtc/build/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/ringrtc/build/linux/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/@signalapp/ringrtc/build/linux/libringrtc-x64.node
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/fs-xattr/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/fs-xattr/build/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/fs-xattr/build/Release/
warning: could not get file information for usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/fs-xattr/build/Release/xattr.node