Refactor SOLiD code into new module under 'platforms'

[pjbriggs]

Moves and reimplements the code for handling SOLiD sequencing data from bcftbx.SolidData into a new module in platforms.solid.data, and from bcftbx.Experiment into platforms.solid.experiment.

The refactoring includes removing the leading Solid from class names (e.g. SolidSample becomes just Sample etc) and changing some method names from camel-case (e.g. getLibraries) to more conventional underscore-separated formats (e.g. get_libraries). (NB SolidRun has been renamed to RunDir.)

The SolidData module has been reimplemented as wrappers around the classes in platforms.solid.data (and the Experiment module as wrappers for platforms.solid.experiment), with the old class and method names still supported for backwards compatibility. It is anticipated that if this PR is merged then the legacy SolidData.py and Experiment modules will be removed.