Feat/conflict popup

[lwray-renesas]

Addressed feature request #1210

Now when there is a conflict (either on startup or after an attempted merge) that cannot be resolved, a popup appears and the view switches to the first conflict to resolve.

Also, previously tool tip erroneously repeated --theirs when hovering over USE MINE
Now it correctly says --ours:

[love-linger]

I've picked the commit 26a4719 manually.

I do not like the Conflict-Popup design. See #1210

And I do not like the idea that always auto-selecting the LOCAL CHANGES page when there're conflicts. There're two reasons:

• In-progress operation may not only due to conflicts, but also empty commits or waiting user to edit commit in interactive-rebase.
• In this PR, every time after SetData being called (generally after SourceGit detected the files in your worktree have been changed), the LOCAL CHANGES will be selected if there are conflicts. Imagine the following situation: when a conflict occurs, the user switches to the HISTORY or STASHES page and copies some content from a certain revision of the file to resolve the conflict. But every time after copying, SourceGit will detect file changes and forcefully return to the LOCAL CHANGES page automatically.