allow user to choose encryption mode

apps/files_encryption/ajax/changemode.php

apps/files_encryption/appinfo/app.php

apps/files_encryption/appinfo/database.xml

apps/files_encryption/appinfo/version

apps/files_encryption/js/settings-personal.js

apps/files_encryption/js/settings.js

apps/files_encryption/lib/crypt.php

apps/files_encryption/settings-personal.php

apps/files_encryption/settings.php

apps/files_encryption/templates/settings-personal.php

apps/files_encryption/templates/settings.php

apps/files_sharing/appinfo/database.xml