package management rework

Architecture:

Problem: RPackage was used by Skeleton/PSI subsystem
and by package management subsystem.
Skeleton/PSI subsystem wanted to create packages on
the fly (skeleton generation, resolve and completion)
while they need only package name and version

On the other hand package management subsystem want to provide RPackage to UI.

Solution:
1) RPackage class contains only name and version
 and should be used only for code insight.
2) RInstalledPackage class contains lots of information including
 custom description fields like Title or URL. It could be passed to UI
 without any conversions.

UI improvements: rework UI in RStudio way
1) description added
2) browse URL action added
3) isLoaded added

TODO:
add unload package functionality

GitOrigin-RevId: 3792b47003a44b901cccc66dbd94d78e4d0e9a8b