Make blocked captures available to revisit resolution

[kngenie]

Blocked captures are often referred to by later revisit captures, and there's a need for making such blocked captures available only for replaying revisit captures.

Internally known as ARI-3879 and ARI-4034.

[kngenie]

Solution introduces new concept soft-blocked captures. While regular exclusion removes capture entirely, soft-block exclusion simply marks capture blocked (indicated by "X" flag in robotflags field).
Soft-blocked captures participate in revisit resolution, but then get removed from final capture search result. This way, soft-blocked captures are made available to revisit replay, without affecting other functionalities, like capture/URL search.

Core functionalities are implemented in commits b0199da .. 0d6dad8 and merged into master in bfe37eb.
Changes so far have been merged to iipc/master as part of 1dbd4f3.

This issue remains open, because there are undesirable side-effects not resolved yet (ex. soft-blocked captures are counted in URL-search results - they should not be).