Updating Math Channel functionality

Currently the user can add math channels manually my clicking Edit>Add Math Channel. This will show the user a window in which they can write their expression and fill other details.

Post processing channels are hard coded and performed similarly on every dataset. The user has no way to update these and they must be updated by the developer. This restricts the users from updating these for changes in the car, year, acquisition method, etc.

The goal is to create a window in which the user can view all active channels including the ones from post processing. These math channels will be saved to a file and loaded in on program start. From this window the user can add, remove, or modify their own channels or post processing channels.

The editing of these channels will use the existing add math channel window that will be refreshed.