[WIDGPT-52]  Add support to use Spring EL in the app launcher URL.
[WIDGPT-52] Add instructions block to config page
[WIDGPT-52] Updates based on code review comments
Merge pull request #11 from jhelmer-unicon/WIDGPT-52_spring_el_for_url

[WIDGPT-52]  Add support to use Spring EL in the app launcher URL.