seminaries/qtmips/qtmips/uart-calc-add: task to receive two decimal numbers from UART and send sum in decimal to the UART.

Implement receive, add and print functions and place C language source
file on path

  work/uart-calc-add/uart-calc-add.c

To run the code in qtmips_cli, the serial port to file redirection
is required. Commit

      qtmips_cli: add option to connect serial port input and output to file.
      https://github.com/cvut/QtMips/commit/597c9271608c3d30ce193b96be3fe82966e4cc1d



qtmips_gui implement required functionality for lonag time already.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>