Fix wrong ScramArch info on view details page

-Fix wrong ScramArch info on view details page: set of values was nicely
hardcoded in the page definition regardless of the actual values in the
request, shows it correctly now

-CMSSWVersion, ScrachArch and GlobalTag were made immutable on this page.
ScramArch could not have possibly worked anyway.

-links from view/details page to Original Config and TweakFile would yield
Server Error 500 if a request was created with ConfigCache document coming
from a host different from where ReqMgr runs (using ConfigCacheUrl argument).
This was fixed too.

Fixes #4249
Merge pull request #4492 from zdenekmaxa/reqmgr-fix-wrong-scramarch-in-view-page

Fix wrong ScramArch info on view details page