Add git functions for sorted listing of branches based on last commit date

[jgogstad]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.

Changes:

Only changes to the git plugin. Two new functions that makes it easy to see what branches you've worked on last, and what branches collaborators worked on last

• gbll: List local branches, sort by commit date
• gblo List branches on origin, sort by commit date

Other comments:

Sample

╰ gblo
2019-07-11 something_some                           John Doe
2019-07-18 address_metrics_feedback                 Jostein Gogstad
2019-07-23 something-else-entirely                  GitHub

Same output for gbll just based on local branches