Use native file dialog for Save As. Fixes crash when no default path
set.
Change Save All shortcut to C-A so it doesn't conflict w/Save As.
Fix default filename.
Fix issue #13 (file open dialog default path)
pothos-gui: delete the old file open dialog
Draw image of block when drag-dropping from block tree.
Correct mouseMoveEvent behavior, no functional change.
pothos-gui: make better use of logging facility
Fix segfault when clicking on blank area of block tree.
pothos-gui: make pixmap stack allocated, fix memory leak
pothos-gui: also fix memory leak with painter
pothos-gui: sharedptr to cleanup block after render
pothos-gui: get bounding rectangle for graph obj
pothos-gui: use prerender and bounds for preview pixmap
pothos-gui: use same render quality for preview
pothos-library: replace port info with a vector of names in creation order
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-gui: use image fill to draw background
Add an extra pixel around the drag render for AA.