Feature: Create hidden markers on GoPro cards

[fxstein]

Create and leave hidden markers on GoPro media cards once various goprox processes have been completed successfully.

For example:

.goprox.archived
.goprox.imported
.goprox.cleaned
.goprox.fwchecked

This enables a quick and easy way to check if and when goprox has performed certain functions against the media cards. The timestamp represents the time the process was last successfully completed.