Allow GUI users to delete registry lockfiles

[HebaruSan]

Motivation

ConsoleUI can do one thing that GUI can't:

It would be helpful if GUI users also had the option to delete the lockfile after an explanatory warning.

Problems

• ConsoleUI's lockfile message confusingly says "instance" twice with different meanings
• The GUI window take a long time to appear at startup (for KSP1); as a rule, the app should be visible as early as possible so users can see it's running, and they should be able to tell what it's doing if it's busy.
• Main's constructor was calling Application.Run, which is not good coding style; a constructor should just create the object (even under RAII), not trigger side effects such as running the entire application

Cause

• GUI calls Registry.Instance before the window appears, which makes it load registry.json which is around 30 MiB nowadays and causes a substantial delay

Changes

• ConsoleUI's lockfile message moved to Core.RegistryInUseKraken.ToString to be shared, and the English text is edited to be clearer (one "instance" is now "CKAN process" and the other is "game folder")
• Now GUI's lockfile error popup is replaced with a yes/no dialog with custom button captions (translations copied from ConsoleUI where available):
  
  If you click Cancel, the manage game instances popup will appear so you can pick a different game instance (if you have any others). If you click Force, it'll try to delete the lockfile and proceed with the chosen instance.
• Now the GUI window appears before registry.json is loaded, and a progress bar is shown while it loads
• The sometimes-slow GameInstance.Scan call is moved from startup to UpdateModsList with its own log message to keep the GUI responsive while it happens (since this was previously between the two progress bar sections)
• We now pass the parent form to all the calls of ShowDialog that I was able to find, which is good practice in case we want to center the child dialogs on the parents
• Main.manager is now private and external users are switched to using the public Main.Manager instead, and various other members of Main are also made private or readonly
• All potentially slow actions are removed from Main's constructor and from OnLoad and moved to OnShown, where they now occur within a Wait.StartWaiting block that shows a progress bar. The roles of these functions are now:
  • Program.Main_: Instantiate the main form, hide the console window, and run the application
  • Constructor: Just set up the basic core properties so Main can be loaded, such as the GUI events
  • OnLoad: Get the GUI configuration (without locking the instance!) so we can get the saved window geometry/layout before the window appears
  • OnShown: Load the registry once the window appears and prompt the user for various things
• GUI configuration is now only saved at exit and when we change instances rather than every time we change any setting
• Main.tabController and Main.Instance are now marked with the [Obsolete] attribute to generate code style warnings, and the Main*.cs file now all have #pragma warning disable 0618 to suppress the warning when used by the same class

This will generally make GUI better behaved, since it will appear very soon after launch and tell the user what it's doing. And if the lockfile exists, users will have the option to delete it.

Fixes #3558.

Deferred to later

We should also show a progress bar when the user changes instances via the manage game instances popup. I looked into that and it was more complicated than I could manage at this point due to conflicting usages of the progress bar tab.

[techman83]

Yep, that will solve a few discord/issue raises. LGTM!