Cleanup ome-release repository (rebased onto develop)



This is the same as gh-110 but rebased onto develop.

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This PR:
- cleans all remaining instances of the Pelican module and the unnecessary `requirements.txt`
- fully rewrites the Readme to list all the currently supported pages and describe the new `make` commands used during  downloads page generation
- cleans some trivial items across the Python files (`hudson` -> `ci` ...)