Provide python handle for parsing yaml files / easy dict generation

[peter-madigan]

A common code geometry-parsing block to extract a channel-to-pixel position mapping is used in a number of different locations, e.g.:

• module0_flow
• larnd-sim
• single-module event display

larpix-geometry should provide a handle for generating some of these commonly used objects, or equivalent functionality. As a start, pixelplane.py contains a class that provides access into the single pixel tile geometry, but was never extended to support multiple tiles. I would suggest that the solution implementation be a higher level class (e.g. AnodeGeo(<multitile layout dict>)) that provides export_XX() handles to provide the dict objects used in the above examples.

@andrewmogan, @yuntsebaryon, @YifanC