note-platform-change takes platform-name now.
Projects now store platform-name.

Projects still store and use the architecture and operating system
slots, this is just an incremental change.
Thread platform-name through project creation.
Project search now takes platform-name.

Since this info isn't used, this change doesn't really mean
anything.
target-platform-name now returns a symbol.
library-description has platform-name.
Update back-end registry to use platform-name.
Remove architecture / operating-system from project-manager.
Finalize changes to switch to platform-name.
Merge pull request #521 from waywardmonkeys/architecture-operating-system-changes

Architecture operating system changes