restructure profile handing

[KitWallace]

need to integrate functional easing profiles with path-based profiles.

Design involves:

• adding a profile 'layer' in Layers
• supporting a set of functions for functional profiles
• using the same profile for layer, scale and rotation rather than 3 different functions
• appling the profile during layer interpolation

Preliminary design work in Fotttery-P.html and fottery-P.js but has drifted a bit for fottery.js

Yet to be decided:

• Handling of open/closed paths (changes basics.js)
• restriction of functions depending on role (perimeter or profile) - circular or linear
• use of profile in interpolation - could use equalise to generate even points so profile access is a simple array access -