Updated pin definitions for UART functionality
Provided a way to set the serial port baud rate.

By letting PlatformSerialP provide the Msp430UsciConfigure interface and implement the getConfiguration method, we can
now pass a different msp430_usci_config_t variable instead of using the default. This is necessary for the EXP430
because the default baud rate table (msp430usci.h) assumes the UART clock input(SMCLK) to be 1MiHz instead of the
correct value of 8MHz.
Removed a #ifdef block that disabled LED2.
Updated gitignore
Inverted Leds.get logic.

I don't know why it was done this way where the ON bits were zeros. I found the
bug when I called call Leds.set(call Leds.get() ^ 0x7). The expected result was
that the three LEDs will toggle. Instead nothing happens. This commit fixes this
by changing the bitwise logic.