Support Rebase

[hdpoliveira]

https://www.mercurial-scm.org/wiki/RebaseExtension

Proposal: three commands in the palette:

• Rebase current branch
• Rebase: Abort
• Rebase: Continue

'Rebase current branch' will display a QuickPick for the destination (-d option), the same as the one used for 'Update to...'. Under the hood, we'll run 'hg rebase -b . -d ${destinationPicked}'
If a conflict happens, we will open the SCM view, and open the first conflicted file in the editor.
The user will be able to run 'Rebase: Continue' if all conflicts have been resolved, or 'Rebase: Abort' to drop the rebase operation.