tree: flatten fw source tree structure
makefile: pass paths to sub-makes explicitly
gdb: remove stray gdb config file
tree: relocate bootloaders to board-specific directories
tree: flatten bootloader updater
makefile: adapt ef targets to new make variables
tree: adapt sim builds to new make variables
tree: move UAVObjects and UAVTalk outside of targets subtree
tree: rename per-board firmware main file to main.c