ISIS-499: Add templates for implementing JDO managed relationships as detailed on:
- http://www.datanucleus.org/products/datanucleus/jdo/orm/relationships.html

Includes support for:
- 1:n bidirectional relationship (implemented using a foreign key).
- 1:n bidirectional relationship (implemented using a join table).
- 1:n unidirectional relationship (implemented using a foreign key).
- 1:n unidirectional relationship (implemented using a join table).
- m:n unidirectional & bidirectional relationship (for the entity acting as the parent).
- m:n unidirectional & bidirectional relationship (for the entity acting as the child).

Added also an "iss" template for creating a new Apache Isis section of code between the "// {{" and " // }} " markers. See the "Code Folding" section of the following URL:

https://github.com/danhaywood/apache-isis-ide