WIP-MEI: UTF-16 files import successfully for both Python 2 and 3

Previously, only UTF-8 files would import successfully in Python 3. Now, we try
UTF-8 first, and if it doesn't work, we try UTF-16. The latter encoding is
produced by the "sibmei" plug-in for "Sibelius," which outputs MEI files.
WIP-MEI: minor cleanup in the subConverters.MEIConverter
WIP-MEI: Improved type detection for MEI vs MusicXML in Converter.parseData()

Previously, parseData() distinguished MEI and MusicXML files by turning the
string into an ElementTree. That was intended to be temporary. Now it's replaced
with checking for "<mei" with the "in" operator. And there's a test!
WIP-MEI: Minor corrections in mei.base

Just removing some errant uses of print() and stuff. Yep---and stuff.
WIP-MEI: Add complicated test file for MEI import

It's quite ridiculous indeed! But you can use it to inspect the music21 objects,
and see that the MEI importer converters everything correctly. You can also try
exporting the imported score to MusicXML and visualize import quality that way,
but several weird things won't be exported properly.

There's also a LilyPond score and PDF output of the intended musical meaning!
WIP-MEI: WIP-1 Tests for measureFromElement()

In step 1, I put the barline-handling code into a helper function called
_makeBarlines(), and wrote tests for that function. Since this stuff is pretty
complex by itself, it'll make testing measureFromElement() much easier!
WIP-MEI: WIP-2 Tests for measureFromElement()

In this commit... I moved the _correctMRestDurs() function's tests into the
TestMeasureFromElement class, since that function should only be used by
measureFromElemtn().
WIP-MEI: WIP-3 Tests for measureFromElement()

In this commit... I added two tests for measureFromElement(), which believe
means the function is ready to go. Heck, I even caught a bug while writing
the tests! (Includes unit and integration pairs)