RFR 8210226: Add support for multiple project folders to idea.sh

[Maurizio Cimadamore]

Hi,
this patch adds proper support for -o option to the idea.sh script, 
which allows to place the .idea folder under any given output folder 
(not necessarily the JDK root).

To be able to do this, I had to revampo the logic for template 
substitution in idea.sh, as it was growing too brittle. I now have a 
much more declarative logic, where replacements can be added by calling 
the add_replacement function. This allows to replace a lot of the 
previous code with very simple and self-explanatory calls to that routine.

This piece was necessary, as we needed to replace a lot of references to 
the idea variable $PROJECT_DIR with the new template variable 
###ROOT_DIR### (otherwise the project is ill-formed, since $PROJECT_DIR 
merely points at the folder containing the .idea project folder).

Webrev:

http://cr.openjdk.java.net/~mcimadamore/8210226/

Cheers
Maurizio