fit-grains calls find-orientations if necessary

This pull request allows `hexrd fit-grains` to call `find-orientations` if it has not already been called. It also adds the ability to load an existing `grains.out` file as the preliminary estimate, skipping the first iteration of `pullSpots` and `fitGrain`, reducing the calculation time by a factor of 3 in initial tests.

A couple additional changes:

1. find-orientations saves its output to the `working_dir`, not the `analysis_dir`. This is necessary to allow multiple `fit-grains` analyses of the same set of orientations (for example, a time series during loading)

1. `find-orientations` output files are now `trial_orientations.dat`, `completeness.dat`, and `accepted_orientations.dat`. This seemed more descriptive and accessible to an end user.

1. some additional logging tweaks to the console to help break up long running operations that may include a call to `find-orientations` followed by multiple `fit-grains` analyses.

1. subclasses `ProgressBar` in order to tweak its `finish` method to delete the progress bar when done.

1. the library itself supports reporting the progress via the progressbar, but it is disabled by default. `hexrd.cli.fitgrains` enables the progressbar, unless `--quiet` is requested. (It is generally bad practice for a library to print statements directly to the console. Instead, it is up to the library to simply emit messages to a logger, and its the application's responsibility (in hexrd's case, the applications in `hexrd.cli`) to configure how logged messages get handled.)

1. adds a required `image_series:omega:stop` value in the config file. Previously calculated the omega stop value from the number of frames loaded by the reader, which introduced too much interdependency in the code. By adding a stop value, we can choose to load and process only a portion (say 120 or 180 degrees) of the data, although this is not yet implemented.

1. refactors hexrd.fitgrains, separating various tasks into functions and making the logic clearer.

1. bumps the version to 0.2.0.dev.