BUILD: Split configure.engines down to a single file per engine.

This is the first part of allowing engines to be added dynamically.
They are placed into a folder in engines/ which must contain a file
named "configure.engine" to add the engine, which is pulled into the
top level configure script automatically.
DEVTOOLS: Factor out function to create directories in create_project.
DEVTOOLS: Adapt create_project for new configure.engine files.

I could not try any generated project files since I do not have access to
the IDEs.
BUILD: Add engines/plugins_table.h to git in the ideprojects target.
BUILD: Add code to maintain ordering of engines in generated files.

This is mainly "cosmetic" to keep the SCUMM engine and subengines at
the top of the various files, but probably a good idea to prevent any
subtle regressions associated with changing the order.
DEVTOOLS: Make create_project sort SCUMM as first engine.

This makes create_project output consistent with configure output again.