Fixed the most frequently occurring deprecation warnings, which were causing over half of the 34,140 deprecation warnings raised during the unit tests:
* `Use of .. or absolute path in a resource path is not allowed and will raise exceptions in a future release` - most of these were due to a single mis-configured resource path with a leading slash.
* `count is deprecated. Use Collection.count_documents instead.` - I added a handful of simple workarounds for this pymongo deprecation that shouldn't increase the query counts
Also did some cleanup of unused code in pavelib after the recent split of the new `i18n_compilejs` command from `i18n_dummy`. (This had caused a diff-quality failure on the first commit.)
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