ModAssistant doesn't refresh modlist after switching Beat Saber Install Folder

[YoukaiTheGit]

After changing Beat Saber's Install Folder in the Options screen, MA doesn't refresh itself to reflect the new installation, including:

• The Game Version dropdown in the lower left
• The list of available & installed mods in the Mods screen

It does reflect the right Beat Saber installation after quitting & restarting the app.

This behavior would make it easier to manage setups where there are multiple Beat Saber versions installed on the same machine. Especially when BS gets an update and trying to manage mods in both old & new installations simultaneously. (This situation would be somewhat easier if #265 were implemented)