Remove "or other" option for stubtreshold

People use this to set it to absolutely insane values.

Enwiki-Stats: http://p.defau.lt/?1j4omOrfCZzQvIJ_z_dOEQ
Change-Id: I88212703c69d0540f3134f661beee6c1428932a9
Merge "Remove "or other" option for stubtreshold"
Add hook to allow extensions to modify the LonelyPages query

First step to solving bug 3483.

Bug: 3483
Change-Id: Ie8c5765ddc6b6028836024c426a0369e6966b25e
Merge "Add hook to allow extensions to modify the LonelyPages query"