Sync supported Gerrits with master

Update Gradle wrapper version in line with Android Studio update

Change-Id: I23c1590a474cee12631d94b827ebf05742a7648c
Endless list sync request fixes

Limit the max number of changes to fetch at once to 100
Detect and block duplicate syncs - don't process new requests
 when the URL is identical to one already being processed
Fix marking of more changes in database
DatabaseFactory: Change insert method to return whether the db
 changed.
Set minimum server version for before/after searching to unreleased
 v2.8.2. This will allow fetching changes to work with stable v2.8.1
 releases and will switch over to the newer searching operators
 when the next Gerrit version is released (even if it is v2.9 or v3.0)
SyncProcessor: insert returns number of rows updated

Change-Id: Ie8add41a340adaced45d9943d7fd4d251a36ce41