fix fill/stroke order bug

[Spongman]

this PR:

• removed the shader.active flag which was getting out of sync, and just uses the existing _doFill/_doStroke style properties instead.
• removed the redundant GL-specific noFill/noStroke methods.
• delays setting the blend stuff until just before the draw call (since it's a global setting shared between fill & edge shaders).
• removes some of the unnecessary usePrograms
• fixes webgl: results dependend on order of stroke/fill calls #2509

[stalgiag]

Great idea! The organization of that section of the code is a lot better now. I don't have an opportunity to investigate deeply. Can you just flag me in some way when you feel that this is ready for a merge? I can run through it then.

[Spongman]

oops, i forgot that i had to exclude the webgl examples from the tests, now that they're actually in the docs. should be good to go now, thx!

[stalgiag]

Cool so I just ran through a bunch of use scenarios and tests. I really like that this now falls in line with using _doFill/_doStroke along with the 2D renderer. Thank you!