[FEATURE] Add functionality to delete a branch

[Jess-Alcantara]

Description
Part of the GitHub workflow includes tidying up your branches. VisualGit should allow you to delete branches after you are done with them.

Acceptance criteria
VisualGit provides the functionality to delete branches from VisualGit locally and on GitHub.

Pointers / Solutions
Deleting branches on GitHub: git push origin --delete <BRANCH_NAME>
Deleting branches locally: git branch -D <BRANCH_NAME>

[Ravid12]

This definitely would be appropriate for any git tool! Approved

[KelseyRM]

Approved - this would be super helpful especially for git beginners that'd want to use VisualGit!

[bcox280]

Approved