Added AttrFilter to ClaimsRequest

This allows server-side filtering of claims by claimtype

Change-Id: I1f5368c17f8f9f59ea0add7df67033447e37bc61
Implemented an optional parameter (attr) in 'camtool claims' to filter by claim type

For example, to obtain all the versions for a given file use:

   $ camtool claims <permanode> --attr="camliContent"

Change-Id: Ibb267a0f95702faa0e7e763c99f99ee446559aac
sorted/sqlite: initialize DB when needed, added test.

Change-Id: Ibd418e357e2bed6a5beed2dda2f947c7c999fe92
Merge "sorted/sqlite: initialize DB when needed, added test."
Merge "Added AttrFilter to ClaimsRequest"
Merge "Implemented an optional parameter (attr) in 'camtool claims' to filter by claim type"
search: escape r.AttrFilter in ClaimsRequest.URLSuffix

Change-Id: I90e5a87330dc6ae820f2f5f6e3887a26f341a2b2