Refactoring of VaspToDbTaskDrone
Allow for more flexible custodianformats (different numbers of runs, etc).
BACKWARDS INCOMPATIBLE!! All classmethods have been removed (and
therefore inheriting classes needs to be adjusted accordingly)
Other changes *should* be backwards compatible, except for edge cases
where extra vaspruns (in addition to relax1 and relax2) are found in
the run folder.
Add option to parse dos from final calculation only. Only add random
vasprun to calculations if none previously parsed.
remove unnecessary documentation
Merge pull request #19 from materialsproject/borg_refactor

Refactoring of VaspToDbTaskDrone, removing class methods