bin/openquake:

Removed --force-inputs option from bin/openquake.
engine2:

Removed `--force-inputs` references in engine2, as well as `_identical_input`.
tests/engine2_test:

Cleaned up tests per the removal of --force-inputs.
tests/engine2_test:

Removed some more test junk.
db:

Removed `force_inputs`/`--force-inputs` references from DB model.
calcs/hazard/general:

Don't use --force-inputs in `initialize_sources`.
calcs/risk/general:

Removed use of `force_inputs` from `_store_exposure`.
tests:

Removed `force_inputs` from a bunch of test code.
bin/openquake:

Cleaned up some --help documentation.
Merge pull request #1093 from larsbutler/remove-force-inputs

Remove --force-inputs feature

[r=matley] [f=1154552]