Created file cache, hooking it up to auth context.

Not currently using it for retrieval.
Using token cache for storing access tokens.

No longer managing access tokens manually, using adal cache logic instead.
account clear removes token cache file

Added token cache file to list of files that are deleted.
Load contents of cache on first access, not at creation time, to avoid
file busy locks when not needed.
JSHint fixes
Updated account show, logout commands

Account show shows presence of a token correctly now.
Account logout now deletes cached tokens for the username that
is logging out.
Updating test suite to mock out token cache.

Fixed bugs.
Adjusted test suite due to API changes.
Setting permissions on access tokens file.

Owner only read/write, nobody else.
Reverting debugging change
Merge pull request #1216 from christav/using-token-cache

Using token cache