Allow optional override for output folder from build.json

[kashiif]

The grunt script always generates output (final wordpress plugin) in 'dist' folder. There could be an optional setting (e.g. dist) in build.json that specifies the output folder. If this setting is provided, create the wordpress plugin files in the specified folder.

[Furqankhanzada]

@kashiif : Can you please add description on it so i can implement it.

[kashiif]

@Furqankhanzada Description updated