Extracts NSOpenPanel extension for creating file choosers, and imports it into SYMFilePickerView.
Hooks up "Finder" file chooser in SYMFilePickerView.
Hooks up the SYMFilePickerViews to SYMAppController.
Shortens SYMFilePickerViews.
Implements user feedback once SYMFilePickerView has a file selected.
Tweaks SYMFilePickerView's constraints.