Implements graph in logging

[stevenguh]

Fixes #38

This PR implements the graph output in logging by executing raw git log commands directly to get the graph output like magit. That allows us to implement many switches that isn't possible with the git api provided by vscode.

Implemented:

• Show graph in log output with a switch (-g)
• Show Author name in log
• Show human readable timestamp on log with date-fn (tree-shaking by webpack should include only that function -- no bloat bundle)
• Implement all log options. l for current, o for other, h for HEAD, L for all local branches, b for all branches, and a for all references
• Implement switches for graph(-g), decoration (-d), and simplify by decoration(`-D)
• Implement rev input box for current (l) option with detached HEAD
• Implement rev input box for other (o) option with default placeholder
• Rev input box allows to log multiple rev separated by , or

Inconsistencies/Features still missing in logging:

• Decoration for log is not as concise as magit. (This requires more input parsing for decoration)
• rev input box do not have autocomplete like in magit. (This can potentially implemented with a QuickPick)
• Color graph (Need to use --color, and needs more input parsing, and a way to display color in a text doc)
• Any switches that requires a follow up input box like -n or -F (This requires more refactoring work with the switch code structure. This refactoring should allow multiple types of follow up input box)
• Reverse (This will be mutually exclusive with --graph)
• Reflog
• Signatures
• Header
• Patch
• Stat

This PR by itself should be ready, I am only listing the missing feature here just to track what else is needed to be done for logging to be feature complete

[kahole]

Looks great :) thank you for covering a big part of the logging functionality
Had cursory look, and I had just have a few comments. I will test the functionality more thoroughly later

[stevenguh]

Apparently stdout can read the color if it is forced with --color; however, there are more input parsing work for that as well as we need to figure out a way to use the syntax highlighting system. Anyway, updated the first comment, so we have a history of it somehow.