Always switch to progress tab when starting a [re/un]install

[HebaruSan]

Problem

If you:

1. Already have some mods installed via CKAN
2. Launch the CKAN GUI
3. Right click an installed mod
4. Choose "Reinstall"
5. Click Yes

... then the progress tab does not display. Instead only the status bar reports progress. Additional odd behaviors and glitches may be observed after this as well.

If you install a mod normally first (before step 3), then it works as expected.

Cause

The sequence of calls needed to use the install flow correctly was:

CKAN/GUI/Main.cs

Lines 971 to 977 in 624839f

	installWorker.RunWorkerAsync(
	new KeyValuePair<List<ModChange>, RelationshipResolverOptions>(
	fullChangeSet,
	install_ops
	)
	);
	ShowWaitDialog();

Previously, the ShowWaitDialog call was missing from reinstallToolStripMenuItem_Click. This call creates or activates the progress tab, depending on whether it already exists, and also does some initialization of the progress bar.

Changes

Now the ShowWaitDialog call is moved to InstallMods, which is the function that RunWorkerAsync calls to do its work. This simplifies the code for installing/uninstalling/reinstalling and fixes the reinstall flow.

Fixes #2343.