Added detector module.

The detector module implements a detector interface and a layered detector
consisting of layers of strips. The detector can be drawn.
Fixed: Need to compare to None with is not ==.
Added track module.
Fixed: strip handling in layer.

Spawns strips with proper y position, only add strip to hit_strips if it isn't
already there.
Added hit clearing to detectors.
Added track module.
Added drawing of hits.
Fixed 2 bugs in Layer.hit: num_strip needs to be an integer and case of hitting the edge of the top-most strip.
Added propagate track to detector.
Draw example tracks along with detector.
Made test for tracking, moved from detector module.
Detector: print hits along with multiplicity of hit.

Also: print on detector positions and hits on seperate lines, added more
explanation to layer hit.
Made track a proper abstract class

Added the unimplemented decorator, and stopped calling the unimplemented init
function.
Added two way Kalman Filter.
Fixed: TwoWayLKFilter returned None on turning point.

Fixed that.
Slight changes to testing functions.
Added track generation function
Tracking test using new track generator.

Works wonderfully.
Stopped printing detector positions.

There are a lot of them and they just spam the terminal.
Fixed layer placements