Add time tracking stats to issue directly from the board

Problem to solve

Time spend or estimated to be spend on an issue cannot be set or seen from the issue boards. Furthermore the time spend cannot be set through commit messages, which are often used to close issues.

Intended users

Developers a.k.a. my-time-managers

Proposal

See and set estimated and spend time of an issue on the board directly. Furthermore allow commands /estimate and /spend in commit messages.