Revert "Maintain the page ID in WikiPage instead of relying on Title"

Related to bug 46427.

This reverts commit c80efe3218c54f0b6fdc971e4a4ffb9ba390df1a

Change-Id: I2dbf8cac53f61662c0c6b8229bfb16b0336a42be
Merge "Revert "Maintain the page ID in WikiPage instead of relying on Title"" into REL1_21