Updated commands used to release the latest IDE.
Updated release sample script with values used for releasing 3.0.1-RC1
Added eclipse profile for building the IDE on Juno/Kepler.
Added the eclipse profile to the toolchain build.
Added building the Play plugin along with the worksheet
Modularizes building plugins, adds Scala-Search

All plugin building optional, default is just building the worksheet (as usual).
Passing a value to the branch for any plugin assumes this branch should be built.
If the branch is empty, the user iw prompted whether

Cleaned up the logic somewhat (branch existence is now tested even for non-interactive input,
plugin repos are not cloned if the plugin is not going to be built, branch asserts fail now before cloning).

This is very much still a rough cut.
Fixes after PR review:
 boolean bugs, conditional p2 merging, ifs, bash substitution