Plot is now a subclass of MapFeature

In preparation for supporting other types of map features:
* Update tiler SQL to be MapFeature-centric rather than Plot-centric
* Update "plot" to "mapFeature" in variable/function names

But don't change the app/tiler interface yet, to keep things simpler until we actually support new feature types.
Merge pull request #29 from RickMohr/topic/plot-is-a-map-feature

Plot is now a subclass of MapFeature
Add jshint configuration file
Fix some typos and bad code style
Continue further in the transition from plot -> mapfeature

Note that this *will* break search queries for properties on plot
(but we don't have any in OTM2)

It is intended to allow searching by tablename in addition to model name
with a later change
Get feature_type in the base and UTF Grid requests for use in styling
Merge pull request #30 from maurizi/topic/map-feature-type-filtering

Allow showing non-plots map features