Basic start on collaborative annotation with Mongo

Implementing via plugin. Right now all one can do is load a feature file into the Mongo database (parameters hardcoded)
Add basic FeatDBObject class

Can wrap IGV features and make some use of them
Add very basic loading of annotation track
Load MongoDB parameters from a config file
Add @api annotations where appropriate to VariantRenderer

IGV-1882
Add ability to add annotations to DB via context menu. Not very user-friendly yet

IGV-2020
Create dialog so user can enter annotation in easier by right clicking and tweaking fields

IGV-2020
Make index creation optional, take advantage of an index if it exists

IGV-2020
Add unit tests for MongoCollab, some refactoring in support of testing

IGV-2020
Add unit tests to MongoFeatureSource

IGV-2020
Add auto start/stop of mongo daemon to unit tests

IGV-2020
Change default mongod path to just mongod; should be picked up if on path

IGV-2020
Set default MONGO_EXEC_PATH in only one place, build.xml

IGV-2020
Fix FileUtils.isTabDelimited so it matches doc; samples first 5 lines and returns true iff there are at least that many tab delimited columns
Add ability to register loader for file extensions to API

IGV-1882
Load annotation track by loading file with custom extension (just added to IGV API)

Only have "add annotation" context menu entry in MongoFeatureTracks, not all feature tracks

IGV-2020
Move FeatDBObject to its own class, rename

IGV-2020
Load plugins earlier in process (in case of custom file loading)

IGV-1882
Use DBFeature.IGVFeat in MongoFeatureSource/Track, so the object being displayed has a backreference to the DB object

This is so we can edit

IGV-2020
Add name field

Add delete functionality to dialog

IGV-2020