Proper implementation of 2D-slits

[MarcusZuber]

TODOs:

• Allow multiple states per Parameterizable
• Add tests for multiple states
• Add some more documentation for the states
• Add slit implementations
  • Slit with 4 motors, each moving one blade
  • Slit with motors moving the offset and gap
• Add tests for slits

About the multiple states:
We use multiple devices, that are composed of sub-devices, where the state-machine can be split in multiple state-machines. Therefore, I introduced the possibility to use multiple states.

class ComplicatedDevice(Device):
   state_1 = State(default="standby")
   state_2 = State(default="standby")
   parameter_1 = Quantity(q.mm, check("standby", state_name="state_1")
   parameter_2 = Quantity(q.mm, check("standby", state_name="state_2")

   @transition(immediate="moving", target="standby", state_name="state_1")
   async def _set_parameter_1(self, p):
       # Do stuff

   @transition(immediate="moving", target="standby", state_name="state_2")
   async def _set_parameter_2(self, p):
       # Do stuff

[codecov]

Codecov Report

Attention: Patch coverage is 91.90751% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 88.48%. Comparing base (b3fbd53) to head (1a630f7).
Report is 10 commits behind head on master.

Files	Patch %	Lines
concert/devices/slits/base.py	88.23%	10 Missing ⚠️
concert/base.py	70.00%	3 Missing ⚠️
concert/tests/unit/devices/test_slits.py	98.61%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #533      +/-   ##
==========================================
+ Coverage   88.36%   88.48%   +0.11%     
==========================================
  Files         120      124       +4     
  Lines        8306     8481     +175     
==========================================
+ Hits         7340     7504     +164     
- Misses        966      977      +11     

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[MarcusZuber]

Tests fail due to race-condition when motion is started. Have to find a elegant solution for this.