Bumblebee-status

Small "hotfix" build:

* Remove built-in 3rdparty `xkbgroup` library, depend on system `xkbgroup` instead
* `layout-xkb` now requires Python3

New modules/features
- Contributed by AntouanK : `currency` module to track currency exchange rates
- Contributed by UltimatePancake : `title` module to show title of current window in the status bar
- Experimental `layout-xkb` for better keyboard layout switching support


Bugfixes
- Contributed by chrismullins : Improved Python3 support for `github` module
- Improved unicode support
- Improved accuracy for `memory` module

Bugfixes
* Fix broken Python3 compatibility for module `datetime`

Improvements
* `cmus` is now hidden when cmus player is not running

Bugfixes
* `cmus` wasn't showing controls (157)
* `datetime` works with non-ASCII locales (158)

New Features
* Experimental dropdown menus using tkinter (contributed by brunosmmm )
* Parameters can be stored in a configuration file now

New Modules
* `nvidiagpu` (contributed by RileyRedpath )
* `mocp` (contributed by chrugi )
* `getcrypto` (contributed by Ryunaq )
* `todo` (contributed by codingo )

Improvements
* Show ICMP packet loss in module `ping` (contributed by dnfm )
* Add weather icons to module `weather` (contributed by dnfm )
* Automatically detect battery devices in module `battery`
* Fewer dependencies for module `sensors` (contributed by ibrokemypie )
* Show remaining time estimate on module `battery` (contributed by yvesh )

Bugfixes
* module `pulseaudio`: Start pulseaudio daemon, if necessary (and if configured)

Apologies if any attributions are wrong or missing, it's been quite a long change list :-)

**New modules**
- sensors - Display temperature (thanks to mijoharas)
- traffic - Show uplink/downlink network traffic per device (thanks to meain)
- stock - Show stock information (thanks to msoulier)
- github - Show number of pending github notifications (thanks to yvesh)
- spotify - Currently playing song in spotify (thanks to yvesh)
- publicip - Shows your current public IP (thanks to RobertSacks)
- bluetooth - Shows bluetooth status and allows toggling (thanks to brunosmmm)
- mpd - Add song information from mpd (thanks to alrayyes)

**New features**
- Add interface status filters for the modules traffic and nic
- Add non-powerline gruvbox theme (thanks to meain)
- Add "scrollable" trait for widgets (e.g. cmus)
- Add logging and a debug mode

**Bugfixes**
- Fix a crash in the xrandr module
- Silence import errors for optional dependencies (thanks to cjlarose)
- Make pulseaudio module robust against localization
- Gracefully handle situations where no weather information is available (thanks to elshize)
- Linting for PEP 8 compatibility (thanks to ibrokemypie)