Revert "SDL: make the default NO_SDL"

This reverts commit 63d1d5457a4e6dd96782ede4bd84035be927fc51.
HISTORY.txt - various updates over the last few months

This is far from comprehensive and people should feel free to further
expand it.
README.md update text

No need to start by focusing on the fork.  We have moved beyond that.
Create static timer instance for UAVO browser. This single timer sets the
rhythm for all highlight events. Previously each class instance had its
own timer and this led to lots of expensives and unnecessary calls to
QTime::currenttime();
Added Qt::UniqueConnection, which ensures that the slot cannot be
connected to multiple times.
Moved currentTime to UAVObjectTreeModel. This eliminates the global and
possible race condition.
Created TreeItem class method for assigning m_currentTime. This simplifies
the number of required constructors.
freertos: pristine import of FreeRTOS 7.4.2
freertos: Re-add our code for accessing the run time information
pios: changed all vPortYieldFromISR to portEND_SWITCHING_ISR
freertos stm32f1 heap1.c: readded xPortIncreaseHeapSize
pios sim: changed all vPortYieldFromISR to taskYIELD
Doxygen: update the module documentation
More module documentation updates
Modules: delete unused magbaro module

Work on #556
Modules: delete unused MKSerial module

Work on #556
Modules: remove unused OsdEtStd module

Used to work for eagletree but the format was undocumented and this
broke.

Fixes #556
Libraries: doxygen header updates

Sorry a few line ending conversions slipped in too
UAVObjectTemplate: update documentation
Doxygen: clean up the outputs