geom_swim_label() Errors

[rsh52]

Description

There are several known errors that occur when calling geom_swim_label() in a few cases:

• Ordering with respect to new_scale_color() and other geoms
• Data inheritance via aes() definitions within a top-level ggplot() call

Proposed Changes

• Add internal capture_error() function for testing only
  • capture_error() is being used to test for equivalent errors between ggplot-vanilla and ggswim. Mostly to help keep a reference of errors that aren't introduced by us (or my fault!)
• Add further handling to try_ggswim() so it returns original error when not a special case
• Add get_mapping_obj() function to capture geom_swim_label() mapping and correctly re-introduce inherited missing params from the current layer

Issue Addressed

Closes #50
Closes #51