Shrimp Shader Generator FLTK2 GUI (SVN)

Reverted back a couple of changes regarding Mantra addition to renderers. Mantra and VEX work should be committed to the dev branch, _not_ main...

Missing curly braces....

Fixed a problem with the Lafortune model, that was using only results from the last lobe. Added the "pump-up" factor suggested by Attila Neumann to the Lafortune model (defaults to original results with p = 0). Added anisotropy support to the coefficients data. Added 29 materials's coefficients, including data from Tek2Shoot's T2SFilePack for Columbia-Ultrecht CURET BRDF database, and some Cornell Universy Program of Computer Graphics ASTM measurements. Changed the usage information accordingly.
Moved all the data from the main Lafortune XML block to the data header (this will be referenced later for user blocks, to allow the user to create N lobes, and define their characteristics as well).

Added Mantra as a supported renderer (to the respective menu entries and renderers.xml - atm duplicated in data/mantra and data/rib). Added some comments regarding RenderDotC status as well. The VEX tags, vex_include and vex_code are supported already, so initial tests and block+headers porting work can start without "unknown renderer" messages.

FIX: fixes in the shader block parser

ENH: first pass to deal with arrays

-logo png format

- Add in preferences : Pixel filter and filter width s ,filter width t parameters
- Add export of Pixel filter ,filter width s and t parameters
- Change color theme of the doc and Shrimp logo: closer to Shrimp color theme

- fix the double display of blocks in the add block menu

Updated some information on the usage for the shadowing and masking functions.