Initial plugin UI support

Use ntk as widget toolkit, as using a light widget toolkit is more
portable than using qt (according to falktx it is not possible to use
qt on windows with LV2 due to shared library issues).
Error out on missing symbols at build time

Better to discover at build time that symbols are missing, than when
loading the plugin.
Add simple LCD display (ntk/cairo implementation)
atom:Blank is deprecated, use atom:Object

See http://lv2plug.in/ns/ext/atom/#eventTransfer
Make LV2 in non-standard directory work

It was not properly adding the include directory for lv2.
Implement notification dsp->gui
LCD fixup
Very basic but working (in Carla) UI
Switch to C++11 for LV2 plugin build

Want to use scoped enums.
Improve LCD display

Light up the area around letters as well.
Improve syx loading and program display