Add template saving to export functionality

Adds the ability to export the current layout as .yaml file. The template is saved in the same format as --gen-template.

To test this, I started with an ndscope screen with only H1:GRD-ISC_LOCK_STATE_N, added two channels to a separate plot, then zoomed out the time axis to change the window size and panned the left plot to turn off autoranging. After that I saved the template, took a screenshot, and loaded the template to compare the plots.

Here is the ndscope screen that the template was saved on:

Here is the ndscope screen after loading the saved template:

The window title, autoranging on individual plots, time axis, channels, and curve formats are the same.