Dialogs/ComboPicker: remove flag bInComboPicker
Dialogs/KnobTextEntry: use "constexpr" instead of macro
Form/Draw: pass PixelRect to callback
Form/ButtonPanel: support symbol button hot keys
WidgetDialog: add method AddSymbolButton()
Dialogs/KnobTextEntry: move event code to new functions
Dialogs/KnobTextEntry: call new functions from button events

Eliminate the complicate double boolean inversion for switching Altair
hot keys.
Dialogs/KnobTextEntry: convert XML to Widget
Form/Edit: move code to EditDataFieldDialog()

Allow debug programs to be linked without all those dialogs, with just
one fake symbol.
KoboMenu: move "Wifi" button to new "Network" dialog
KoboMenu: add "telnet" button
Kobo/System: add function IsKoboWifiOn()
Kobo/System: background udhcpc
Kobo/System: kill udhcpc
OS/Process: new library to launch sub processes
Kobo/System: use new OS/Process library

The library doesn't invoke the shell, and thus reduces overhead.
OS/Process: unblock all signals before executing

Due to our use of signalfd(), we had to block SIGTERM and others.
This is a big problem because the signal block mask is inherited to
child processes, and persists even execve().
KoboMenu: don't disable Wifi on startup

Leave it in whatever state it was in previously.  By default, Wifi is
off on boot, and that's just fine.
OS/SocketAddress: support AF_LOCAL
Kobo/NetworkDialog: rename WIFI to TOGGLE_WIFI