Implemented resume command

[zealot128]

I've added a first version of the "gtt resume" command.

When working on a project and have to switch contexts, like fixing a bug in another project, then returning to the original work, this commands "resume" the tracking.

cd project1/
gtt start SOME_ISSUE
# ...do work

# get interrupted for urgent bug fix
gtt stop
cd project2/
gtt create "fixing bug"
# fixing bug...
gtt stop

# returning to project
cd project1
gtt resume

This is a first version of the command, I may have not considered all usecases. Instead editing/reoping the original entry, a new edit is created. Please comment on the code, where you like to do something else or throw it away entirely :)

I like to use a .gtt.yml file per project, so specifying the --project parameter via commandline is not necessary for me, as that is assumed from the config. If the user does not have a .gtt.yml, the last entry will be recontinued. Also useful for breaks, etc.

[coveralls]

Coverage remained the same at 78.344% when pulling e7d8c01 on zealot128-os:gtt-resume into 8c835d7 on kriskbx:master.

[coveralls]

Coverage remained the same at 78.344% when pulling acade2b on zealot128-os:gtt-resume into 8c835d7 on kriskbx:master.

[kriskbx]

This is a cool and very useful idea. I really appreciate your contribution. Just gimme some time to look into it and try it out. :)

[kriskbx]

I merged your PR but did some refactoring so the code looks a bit cleaner. Thank you so much for your contribution, I really appreciate it. I will release a new version of gtt containing this feature within the next few days.

[zealot128]

that's great. Thanks for the making this project :)

[kriskbx]

You're welcome. :)