Add support for JSON TSR and TSRChain serialization

[mkoval]

This package currently uses the CBiRRT space-delimited format to serialize TSRs and TSR chains. This format is not clearly documented anywhere and is quite error-prone to implement.

The newer pr_constraint_or_ompl package uses a JSON format, instead. As @psigen suggested in personalrobotics/prpy#311, we should add support for this JSON format to or_ompl as well. Once we have done so, we can deprecate the CBiRRT format.