fix subMgsaSets()

- items parameter is a character vector of ids
- original item ids are preserved after subsetting
- item and set annotations are preserved
enhance getting item/set annotations

- require exact name match
- always return data frame
add tests infrastructure using testthat package
add subMgsaSets test
draw lines in parameter distribution plots
First version bump prior to creating 2.14 branch.

git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/mgsa@88838 bc3139a8-67e5-0310-9ffc-ced21a209358
Second version bump after creating 2.14 release branch.

git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/mgsa@88840 bc3139a8-67e5-0310-9ffc-ced21a209358
Merge branch 'fix-subset' of https://github.com/alyst/mgsa-bioc
Suggest the testthat package.