Several improvements for the Welcome/Repositories page

[goran-w]

• Unify all file-path normalization, to use char-replace (instead of string-replace) and to trim any trailing slash.
  • Removing (if present) the trailing slash in paths is needed to avoid failing comparisons, since DirectoryInfo.Fullname (and .FullPath) will not "normalize" the presence/absence of a trailing slash, making any direct equality tests error-prone.
  • This fixes a bug in ScanRepositories.GetUnmanagedRepositories(), where not all Git repo folders were added.
• Refactor the sorting of the RepositoryNode tree, to use a single method instead of duplicated code.
  • Also make the sorting of the RepositoryNode tree case-insensitive, to make items easier to locate.
  • Sort & Save the whole RepositoryNode tree after a complete rescan, to make sure it's fully consistent.
• Activate TabsDropdownItem on Tapped instead of DoubleTapped, for easier access.
• Bug-fix: Prevent exception in Repository.RefreshBranches(), for repo which has no commits/branches yet.
• Correct spelling error in App.GetLauncher() method.
• Correct a variable name from 'founded' to 'found'.

[love-linger]

I've manually cherry-picked partial of commits in your PR.

Commit 663567e is not picked. I think sort by name in case-sensitive way is more common than case-insensitive and I really do not like it. For example:

A
a
Ab
ac
ad
Ae

BTW. Next time, please don't submit so many commits (for different purpose) in a single PR. It's difficult to tell from GitHub which changes correspond to which commit. I can only cherry-pick each commit manually and then review. It's too tiring.

[goran-w]

Thank you. I'll use fewer commits and more concise PR branches in the future. But also, you could've asked me and I would have removed the unwanted commit from my PR branch. 😉

However, personally, I find case-sensitive sorting very frustrating, since bee is not located between Beat and Bell in the example below - I have to look through two "sections" of the list to find it...

Art
Beat
Bell
Boo
Cow
Deep
Early
Far
arty
bee
cee
dee
fee

So at least it should be made a global Preference "Use case-insensitive sorting in all lists" (or similar)!

Let's close this PR, I'm working on a new one for optional case-insensitive sorting (including some bug-fixes). 😬

[goran-w]

Follow-up PR for case-insensitive sorting Preference option: #1401

[goran-w]

For reference, the commits cherrypicked from this PR were:
f04b0c5, 75c32c1, 54c05ac, 88c38b4, b969ac1, 406ace9
(Also, commit 464fe74 was a code review for b969ac1.)