Graph Markers, Version 2

[jlitewski]

Did a decent overhaul of the Graph Markers (again, but this time with more features!)

• Moved things around again. The four main markers (A through D) now live in proxgui instead of ui
• Implemented the marker_t struct, which currently holds a marker's position and it's label
• Added the ability to set Temporary Markers
  • These Markers are only set in code (for now), and are for things like marking noteworthy positions on the graph (like the start of a bit)

Oh, I also fixed a few memory leaks I accidentally introduced 😅

If you want to see what a full implementation of this updated marker system can do, load lf_TI and demod it.