Consolidate parameter handling, expose reconstruction stage parameters

[Ylannl]

This overhauls reconstruction parameter handling and allows user to control them through the config file. Fixes #123.

TODO:

• harmonise all angle parameters to use degrees as unit
• harmonise all snapping/distance thresholds to use simple distances instead of exponents
• Review the documentation
• Introduce parameter scaling factor to handle non-metre units (fixes Add option to set unit to feet #144 and Add a scale parameter, to better handle low density pointclouds #169)