replace coffeescripted-sbt plugin (it was too slow)

it was too slow because it used Rhino.  so instead, use custom code
that installs the right version of the CoffeeScript compiler in the
local node_modules directory and then runs it as external process. way
faster.

as a bonus, we get a newer CoffeeScript version (1.6.3 instead of 1.2.0)

fixes NetLogo/Tortoise #32
fixes NetLogo/Tortoise #33
Merge remote-tracking branch 'origin/tortoise' into coffeescript-via-node-not-rhino

Conflicts:
	project/Tortoise.scala
minor cleanup
Minor improvements to 'Coffee.scala' build file
Merge pull request #494 from TheBizzle/coffeescript-via-node-not-rhino

Minor improvements to 'Coffee.scala' build file
check exit code of CoffeeScript compiler

so if compilation fails the task fails
Merge pull request #490 from NetLogo/coffeescript-via-node-not-rhino

replace coffeescripted-sbt plugin (it was too slow)