Adding dictionary storage for #319.

[theacodes]

• DictionaryStorage - implements an optionally-locked storage over a dictionary-like object.
• Moved optional locking logic into Storage, previously this has been duplicated in subclasses.
• Removed flask_util.FlaskSessionStorage and replaced it with DictionaryStorage.

[theacodes]

Looks like the django tests are hurting me. I'll rebase once the django fix (#350) is in.

[theacodes]

Sigh, failing for different reasons now, I'm going to have to modify the django_util's storage class. I'm going to hold off until #353 is done. No need to make this change while we're still shuffling code around.

[dhermes]

@waprin and I had discussed (1, 2) this a bit. I think the Django Storage is borken so that might explain it?

[dhermes]

@jonparrott I killed the build
https://travis-ci.org/google/oauth2client/builds/100446260
to move #378 to the front of the line (since it is a critical error).

I'll try to restart it once #378 is merged and tests have run there.

[theacodes]

@dhermes 😢

I definitely wasn't waiting on that for the last hour or anything.

I'll just continue my crusade against httplib2.

[dhermes]

Haha it seems Travis is batching us to one job at a time so hopefully yours will be the one and only and will start right up.

[dhermes]

@jonparrott #378 has finally been merged (tests ran at 7:45am Pacific today, 18 or so hours after being created, oy). You should rebase so that your tests don't fail on Python 2.6 (I can restart the original build if you want, but it was going to fail on Python 2.6)

[theacodes]

Rebased. Waiting on Travis.

[theacodes]

Don't review yet. I'm breaking this up into smaller changes.

[dhermes]

Yay!