Add search functionality to pothos-gui.
Search fast. Cache JSON data on init so search doesn't have to reconnect.

Left the QTimer infrastructure in place in case search gets slow later.
pothos: use async futures to speed up module load
pothos-gui: use image fill to draw background
Add an extra pixel around the drag render for AA.
Merge branch 'master' into port_work2
pothos-library: moved auto port allocation to port allocation cpp