I3-resurrect

Fixes:
- Made corrections to reflect upstream changes in i3ipc-python

Fixes:
- Fix bug saving terminal emulator working directory

Enhancements:
- Rework `window_command_mappings` config parameter to make it much more flexible
- Add `window_swallow_criteria` option to allow specifying swallow criteria on a per-window basis
- Add unit tests
- Add command tests (using tox)
- Integrate with Travis CI and Coverall
- Add `--version` option
- Improve command help text

Fixes:
- Terminal emulator cwd is now retrieved from the terminal's first subprocess instead of window title
- Set PWD environment variable as well as cwd, because a lot of applications use the PWD environment variable for things

Enhancements:
- Switched from os.path to pathlib
- Add --layout-only and --programs-only options to save/restore commands
- Implement deferred swallowing using xdotool to unmap and remap windows so that matching by window title can work properly
- Change the way windows are looped through when saving programs
- Update documentation (including a gif demonstrating usage)

- Add --swallow option which allows the user to specify swallow criteria
- Stop using i3-save-tree and instead build workspace tree manually using i3ipc

- Switch subprocess i3-msg commands to use python-i3ipc instead
- Fix bug where restoring multi-word workspace names fails due to improper quoting of arguments