update conda-store-ui to new default port

[dcmcand]

Fixes #322

Description

Updates the default conda-store-ui port to be compatible with new conda-store-server default port. Although conda-store-server is configurable which port it runs on, and webpack will increment the port if 8080 isn't free, this PR removes the inherent conflict in ports. It also stops conda-store-server from running on port 5000 which is problematic for Mac users.

This pull request:

• Set default conda-store-ui port to port 8000
• Update conda-store-server use to use new default port of 8080
• Define port for conda-store-ui to run on in webpack.config.js

Pull request checklist

• Did you test this change locally?
• Did you update the documentation (if required)?
• Did you add/update relevant tests for this change (if required)?

Additional information

[nkaretnikov]

@dcmcand I've left some comments regarding unrelated changes. Please ping again once those are resolved and I'll test locally. Thanks!

[nkaretnikov]

@dcmcand LGTM!

Tested with (was able to log in/out and build an env):

# server
python -m conda_store_server.server --standalone --config config.py

# ui
yarn run start 

config.py:

# This MUST start with `/`
c.CondaStoreServer.url_prefix = "/conda-store"

server: 0760fa2
ui: cf6a34f8b9a44f6c10c9466ac423852373d52168, base: b4a5b46732f3441084fff4ff5537d494f0f3f09e

The config won't be necessary once conda-incubator/conda-store#647 lands.