FEATURE: Allow overriding the LockHoldingPage via environment variable
FEATURE: Allow overriding the LockHoldingPage via environment variable

You can now specify the environment variable FLOW_LOCKHOLDINGPAGE in order
to override the path to the page shown, when the site is locked, relative
to the FLOW_ROOT_PATH.

Resolves #585

robertlemke/flow-development-collection,dlubitz/flow-development-collection,dlubitz/flow-development-collection,bwaidelich/flow-development-collection,kdambekalns/flow-development-collection,albe/flow-development-collection,kdambekalns/flow-development-collection,robertlemke/flow-development-collection,neos/flow-development-collection,albe/flow-development-collection,fcool/flow-development-collection,kdambekalns/flow-development-collection,fcool/flow-development-collection,bwaidelich/flow-development-collection,neos/flow-development-collection,bwaidelich/flow-development-collection,fcool/flow-development-collection,robertlemke/flow-development-collection,robertlemke/flow-development-collection,daniellienert/flow-development-collection,neos/flow-development-collection,fcool/flow-development-collection,neos/flow-development-collection,daniellienert/flow-development-collection,dlubitz/flow-development-collection,albe/flow-development-collection,daniellienert/flow-development-collection,kdambekalns/flow-development-collection