Updating Mixpanel to 4.3.0.

Updating to latest version of Mixpanel as they patched it to allow us
to get access to super properties which will allow us to properly
track them.
Fixed bug where we were wiping out all of our super properties.
Merge pull request #1769 from wordpress-mobile/issue/fix-broken-superproperties

Issue/fix broken superproperties
cherry picked 65beeb114c392d6c931ef928ef939130bdfaca20
add ABTestingUtils
Merge pull request #1770 from wordpress-mobile/issue/helpshift-workaround

helpshift workaround
remove the _contact us_ button from preferences (it's already in Help and Support)
Merge pull request #1771 from wordpress-mobile/issue/double-contact-us-button

remove the _contact us_ button from preferences (it's already in Help and Support)
3.1-rc-1 version bump
use new utils version
fix a merge conflict in zbetagroup
Squashed 'libs/utils/' changes from 449639d..f75a9e7

f75a9e7 increment version number
44bb61e Rewrote the AppLog viewer to use a ListView+adapter
59f0bfa Merge branch 'develop' into issue/1690-track-last-seen-screen
9300d28 remove unused util file ActivityUtils
b15cf64 Bump libs/utils version number.
0d89a80 generic way to track last seen activity - requires GET_TASKS permission
391276c Use the unicode version of the Horizontal ellipsis char. Restrict the visibility of some methods to private.
c8dc1e8 Text view that auto adjusts text size to fit within the view.If the text size equals the minimum text size and still does not fit, append with an ellipsis.
aa5b665 init utils readme
76df52f import libs/utis

git-subtree-dir: libs/utils
git-subtree-split: f75a9e71abcbb70a4e46cd7f436ff92fb957dc81
Merge commit '3a77c01015919f187852c63c384d9a2a48421d24' into release/3.1

Conflicts:
	libs/utils/WordPressUtils/build.gradle
Merge branch 'release/3.1' into develop