Implements the handling of arbitrarily complex data structures.
The following are supported:
- Lists (like `key:[val1|val2|...]`)
- Dictionaries/Maps (like `key:[k1:v1,k2:[v2a,v2b]]`)
Lists of Dictionaries/Maps look a bit different:
```
key:[k1:v1,k2:[v2a,v2b]|a:x,b:y]
\_______________/ \_____/
dict1 dict2
```
* Added a context menu on the buttons including Clear & Restore Default
* Allow clearing (unsetting) inputs. Added a Clear All button
* Allow restoring a single input to default (instead of all)
This avoids a redundant std::string construction if a key doesn't exist
in the map already.
e.g.
data[key] requires constructing a new default instance of the value in
the map (but this is wasteful, since we're already setting something
into the map over top of it).
