Attempt to handle lack of account picker on device
Handle loading of account in base activity

Eventual goal is to ensure that any DroidBooruAccountActivity subclass has
access to an account as soon as the subclass' lifecycle is triggered
(particularly after first launch when the user is required to pick an
account). Currently the activity is allowed to run in the background of the
account picker. A better solution is desired.
Remove project.properties
Reorganize activities

The app can now be entered from either the Gallery or UploadFiles activities,
depending on what function the user activates first. If an account hasn't been
selected, the user is prompted immediately.

Backend.getInstance() now requires a Context, but this allows it to be
instantiated at any time if necessary, which is important for the above app
flow changes.
Use US locale when formatting date in default tags
Resolve AccountPicker intent before using it
Merge pull request #7 from cwc/accountPicker

Handle loading of account in base activity