Update gradle for new AndroidStudio and SDK

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>
Replace Dropbox Sync API with Core API

Sync API kept producing Sync Conflicts, even though both versions of the
file were identical. The Core API allows pure overwriting.

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>
Reversed due time change

Include ability to select due time

Signed-off-by: Jonas Kalderstam <jonas@kalderstam.se>