Added a Singleton VaultHolder with weak references to Vaults
This should allow the app to share a Vault over different views without
re-creating the vault with the expensive PBKDF2 operation.

It is crucial, that the VaultHolder is cleared when leaving a Vault,
otherwise this might still be accessible without the correct password.

This concept has to be reviewed!
Modified VaultHolder to hold only one Vault.
The currently loaded Vault can be retrieved without the name or password.

Every invocation with name and password clears previously loaded Vaults for
security reasons.
Merge pull request #27 from L-Henke/vaultHolder

Added a Singleton VaultHolder with weak references to Vaults
Updated Apache Commons IO dependency
Vault rename moves directory instead of copying it.
This is much faster for large Vaults
Merge pull request #28 from L-Henke/apacheCommonsUpdate
Upgrade API to 5.0, with changes to make app run.
(UI still needs slight modification)
Fix Iab-related crash in 5.0
(Explicit Intent Required)
Update ActionBar title according to new API
Fix crash when changing to gallery
Styling dialogs accord Material specs
Remove fake actionbar in updatemanager
Moar materialllss
Merging with new encryption engine