Migrate Firefly's onlinehelp system so that it can be used by SUIT.

• created github repository: https://github.com/lsst/suit-onlinehelp/
• copy content from existing irsaviewer online help.
• change build/config script for SUIT.
• setup build/install environment for pdac

To build and install online help on pdac:

• log into sui-tomcat01
• switch to suiadmin
• source /hydra/cm/env/env.sh
• cd /hydra/cm/suit-onlinehelp
• git pull
• gradle install