XD-953b: module options take2

Like https://github.com/spring-projects/spring-xd/pull/356, only different

Currently has support for the "simple" case with keys of the form
```
options.<module>.description (mandatory)
options.<module>.default (optional)
options.<module>.type (optional)
```
Note that "type" is now used for documentation purposes only, there is no actual typing computation done.

Cherry-picked the module info command from other PR

Pending issues (to be addressed in another PR):
- complex case
- default values for complex case, when option is not surfaced back to the module (eg "suffix" in our canonical example)
- plugin provided options and values
- descriptive defaults instead of actual defaults (e.g. <use stream name>)