Stop flake8 complaining about too long lines

Although PEP8 generally advises to use 79 characters, there is an exception
given:

> Some teams strongly prefer a longer line length. For code maintained
> exclusively or primarily by a team that can reach agreement on this issue, it
> is okay to increase the nominal line length from 80 to 100 characters
> (effectively increasing the maximum length to 99 characters), provided that
> comments and docstrings are still wrapped at 72 characters.

Hereby, the limit is lifted to 99 characters and flake8 stopped from being
complaining. If you need longer lines, consider refactoring your code by writing
functions or store intermediate results in variables.
Add parameter descriptors

Instead of having the implementor install parameters at run-time, they now have
to be part of the actual class. This allows for a cleaner and more robust
implementation.
Fix conversions and use motor mixins
Rename Motor to LinearMotor
Fix quantity conversion
Use default position and velocity calibration

This includes reverting the velocity in dummy motor from q.count / q.s
to q.count
Allow dummy continuous motors to be stopped

The MRO of the mixins prevented that.
Make dummy focusing tests more robust

by not enforcing the unit to be mm in the out of limit tests
Implement state machine transitions for Parameters