Issue mozilla-mobile#2338: Bump version to v3.10.

There was a merge conflict when trying to cherry-pick the CHANGELOG so I
decided not to do it: the CHANGELOG on master is the canonical state.

Author: mcomella

app/build.gradle

@@ -25,7 +25,7 @@ android {
         targetSdkVersion 28
         versionCode 11 // This versionCode is "frozen" for local builds. For "release" builds we
         // override this with a generated versionCode at build time.
-        versionName "3.10-LAT4"
+        versionName "3.10"
         testInstrumentationRunner "org.mozilla.tv.firefox.FirefoxTestRunner"
         testInstrumentationRunnerArguments clearPackageData: 'true'