Bug 56704: Allow mobileview api to handle section ranges

Alternative solution to https://gerrit.wikimedia.org/r/#/c/94093
Allow users to request ranges such as sections=3-5|7|8 - same as 3|5|7|8
'sections=1-' means from section #1 until the end

Change-Id: I425320b92cbfc837acaf5f4445e7fd3c66280eb6
Merge "Bug 56704: Allow mobileview api to handle section ranges"