fixed #32: calc wOBA with season coefficients

Added statsConstantsService to store yearly coefficients for wOBA and
FIP. We can store other historical seasonal coefficients here as well.
The last statsYear of the filter is passed to calculateResults and
stored in results. Then getCoefficients(results.year) fetches the
coefficients.
Add calcWRAA using wOBA scale

Add calcWRAA and store wRAA values in results. Also edited some
calculation function comments to be more consistent. wRAA is not live on
pitches tab yet, just calculated in case we want to add it.
#32: jshint/javascript refactors
replace angular-strap with angular-bootstrap in the bower config
#42: slight code reorg