front: De-anonymize the AsyncTask for computing file hashes.

Re-usable and arguably easier to read.  Also enforces input contract.
front: De-anonymize the AsyncTasks for refreshing ROM cache.

Re-usable and arguably easier to read.  Also enforces input contract
and follows same idiom used elsewhere regarding async tasks.

Obsoletes the RomCache class.
front: Follow same AsyncTask idiom for extracting hi-res textures.

For consistency and to enforce input contracts.
front: Implement asset extraction as an AsyncTask.

Easier to read and follows same AsyncTask idiom used elsewhere.
Enforces input contract and doesn't require programmer to understand
UI/non-UI thread relationships.
front: Do some ops only if assets were actually extracted.

Mostly just logical hygiene.  Also eliminates message when assets don't
need to be extracted.
Merge branch 'refactor/async-tasks'