Allow run external mode with higher rates

This change solves data exchange issue with higher model rates in
external mode.  Standard SYS/BIOS Semaphore was repleaced with binary
semaphore this will prevent from semaphore overflow.
Change in mdaq_net.c is still workaround, socket driver which is used
for data exchange will be redesigned to handle different DSP requests.
DSP autostart

In order to upload DSP binary on MicroDAQ user has to double click on
block UPLOAD from MicroDAQ block library. DSP binary will be saved on
non-volatile MicroDAQ memory and will be executed automatically on next
power on cycle. UPLOAD button will save DSP appliaction already loaded
on MicroDAQ after e.g. executing Build Model operation.
User can access DSP appliaction via user disk, in 'dsp' directory one
can find file dsp-firmware.out which is DSP application which is saved
and started on every power up.
In order to turn of autostart of DSP application simply connect MicroDAQ
with USB cable and delete dsp-firmware.out from user disk.

Note that only standalone DSP appliactions will run without Simulink.
Divide socket driver from RPC stuff

This is first step to make more general approach for handling sockets,
files etc.
Initial support for UART

UART support has following limitations:
- all UART blocks doesn't work with external mode - standalone mode only
- only one UART module can be used in model
- flow control isn't supported at the moment