Speed rename

This fixes Bug https://bugs.launchpad.net/mixxx/+bug/1283190
Pitch-bend in the DJ context is different from the keyboard context -- there's precedent for calling pitch-bend / tempo-bend a button that increases/decreases the speed temporarily. On old turntables the pitch bend buttons ran the motor faster or slower. CDJs copied that but added master tempo and either still called them pitch bend or called them pitch/tempo bend.

We provide parenthetical / slashed text to give the user a hint for terminology they might be used to. An example is "headphone (pfl)" above so it may be useful to keep "pitch bend" in the string because people are used to calling this a pitch bend.

What about:
"Temporarily Increase Speed / Pitch Bend (coarse)"
"Temporarily Decrease Speed / Pitch Bend (coarse)"
"Temporarily Increase Speed / Pitch Bend (fine)"
"Temporarily Decrease Speed / Pitch Bend (fine)"