Update Gobra to the newest Viper version

[jcp19]

This PR updates Gobra to use the latest changes as of today (01.09.2022). Initially, it was meant to update Gobra to use the viper version from the 22.07 release, but instead it uses a more recent version than that due to nice-to-have changes made recently (in particular, viperproject/silver#604).

Furthermore, in this PR, I removed ViperChopper - instead, we now use Chopper provided by silver. Furthermore, I changed Gobra to use submodules, which makes the process of upgrading and installing Gobra a lot easier! Thanks @ArquintL for changing viperserver to use modules.

[ArquintL]

@jcp19 ViperServer (i.e. the master branch) is now using submodules. It should thus be sufficient to only have ViperServer as submodule

[Felalolf]

I am not sure it is the best idea to make Viper Server determine which Silicon, Carbon, and Silver version Gobra uses. That said, I guess we can still pick individual Silicon, Carbon, Silver versions by creating a ViperServer branch with the set of depencies that we want.

[ArquintL]

Please remove the following entries from .gitignore:

carbon
silver
silicon
viperserver

[ArquintL]

I am not sure it is the best idea to make Viper Server determine which Silicon, Carbon, and Silver version Gobra uses. That said, I guess we can still pick individual Silicon, Carbon, Silver versions by creating a ViperServer branch with the set of depencies that we want.

I think it's good that ViperServer determines the dependent commits since this is tested & guaranteed to work. We'll typically either use a Viper release (with fixed commits for ViperServer, Carbon, Silicon, and Silver) or a nightly release of ViperServer. In the latter case, the current master version of Carbon & Silicon is used & tested (while updating the corresponding submodules)