Add framework for multiple custom accounts

This patch adds custom DroidBooru accounts. Such an account is created by
asking the user to choose a "com.google" account (since nodebooru uses
Google auth, and DroidBooru doesn't really auth yet anyway).

Also removed old concept account code (LoginSettingsActivity, etc.).
Add basic account creation

This patch allows the user to specify a Google account, server address,
and name. The information is stored as a custom DroidBooru account.
Set server address input type to URI
Change base class of CreateAccountActivity
Name Nativ DB according to server address
Remove Nativ submodule; use nodebooru's instead

Also updated the Nativ libs and changed nodebooru ref to a custom
build.
Support multiple accounts and account switching
Merge pull request #10 from cwc/accounts

DroidBooru account support