Fixed bug with formatDateRange()

If the start/end times are exactly the same, we should leave them
that way so they end up representing a single point in time rather
than a range.
Added getRelativeTimeSpanString() w/ preps and tests
Added translations for getRelativeTimeSpanString() w/ preps

From AOSP
Removed excessive parameterization of methods

Having methods that mixed ReadablePartials/ReadableInstants was a bit
overkill.  First, it cluttered up the class, making it harder to tell
what method you wanted to use.  Second, its behavior is too random.
Depending on what partials you pass in, random fields get filled in
between it and ReadableInstant it usually needs to be converted into.

By keeping everything partial or instant, we have a grounding for
comparing the parameters and keep things a bit more succinct.
Removed "now" parameter from getRelativeTimeSpanString()

It didn't make sense that you'd need to pass in "now" when you
always want to compare the time to the current time.

By getting rid of it, it makes the API a lot easier to read/understand.

Also expanded test coverage to cover all API calls related to
getRelativeTimeSpanString()
Made tests much more consistent

Basically, the left side (what the assertion should equal) is mroe hardcoded.
This means that the tests have a consistent output they should be doing.

Most of this was achieved by setting a consistent "now" time for all tests
that doesn't vary.

The only place where this wasn't done is where the output can be platform
specific, e.g. formatDateRange() isn't fully implemented in our own DateUtils
and depends on Android.
Up getRelativeTimeSpanString() min resolution

Don't switch on an interval just because we're off by less than a second.
Added getRelativeDateTimeString() and tests
Added translations for getRelativeTimeSpanString()
Reformatted code automatically
Updated to latest build tools/plugin
Removed joda-convert as dependency
Import joda-convert whole-hog

We need to use our own local version that does not use javax.xml.bind
Remove reference to javax.xml.bind
Bumped minSdkVersion

Turns out joda-convert needed minSdkVersion 9 for Arrays support
Changed lint options

- We get rid of that error ourselves from org.joda.convert

- We also have to ignore MissingQuantity as not all translations are
  perfect from AOSP.
Updated versions to 2.3.1
Added local version of gradle-mvn-push

So we can make modifications
Add android runtime jars to javadoc list

Otherwise we get errors during javadoc task