Envelope pitch feature

[Demo of Pitch Envelope in FL](http://youtu.be/cyuVEK--pPo?t=4m45s)

**Pitch Envelope thoughts**
- Although we already can control pitch within an instrument, It has to be automated to achieve what a pitch envelope can achieve.
- Pitch Envelope will allow for creating more complex instruments ( for sharing ).
- This will work using the same ADSR settings available already in the ENV section of Plugins.
- Basically the structure already in place for pitch bending will be used. There may need to be a selectable range from [1] to [24] the same as in the Plugins main window.
- I'm unsure of where the starting point would be according to using an attack, e.g does the pitch start at it's lowest possible pitch within the range or does it start at the base frequency and if so can it be set to work both ways ( from zero to max or zero to min ) when needed?

_edit ... my git formatting sucks_

Start by locating the existing pitch-bending implementation and the plugin ENV section that provides ADSR settings and selectable pitch ranges. Resolve whether the envelope starts from the base frequency or a range limit, and whether both upward and downward modes are required. Done means the feature's behavior and scope are specified before implementation begins.

Written by the indexing model from the issue text.