[MIDI import] Use words instead of fractions for quantization note values

Where:
File > Open and select a MIDI file, then click on the Quantization pull down menu

Menu should read:

Value from preferences
Shortest note in bar
128th
64th
32nd
16th
Eighth
Quarter

Menu actually reads:

Shortest note in bar
Value from preferences
1/4
1/8
1/16
1/32
1/64
1/128

Discussion: Basically there are two differences.

1. The note values are spelled out as words rather than mathematical fractions. This is how note values are usually written in American English text. It also matches the note values elsewhere in MuseScore (including tooltips on the Note Entry toolbar and relevant pages of the handbook). I find it easier to read.
2. The note values follow a logical order from smallest ("Shortest note in bar") to largest ("Quarter"), and the default value ("Value from preferences") is the first menu item instead of the second.

The quantization menu in Edit > Preferences > Import has similar issues.

MuseScore version: c4e95c7

(Operating System: Windows 7)