Add @todo API and describe ol.geom.Geometry funcs

The `clone()`, `getSimplifiedGeometry()` and `getType()` methods are all
base class methods documented in subclasses.  They should appear in
ol.geom.Geometry in the API docs as well.
Document that feature properties are set as object properties
Document that layer options are set as object properties
Merge pull request #2298 from probins/props

Document that options in layers and properties in features are set as object properties
Merge pull request #2177 from pagameba/geometry-api

Add @todo api and describe ol.geom.Geometry funcs