Geo bounds aggregation support

Closes #822
Remove unnecessary JsonObject attribute
Merge remote-tracking branch 'origin/feature/aggregations-geo-bounds' into develop

Conflicts:
	src/Nest/DSL/Aggregations/AggregationDescriptor.cs
	src/Nest/Nest.csproj
	src/Tests/Nest.Tests.Integration/Aggregations/MetricAggregationTests.cs