RF2500T board and pins

Adding support for eZ430-RF2500T w/ MSP430F2274.

The MSP430F2274 is part of the MSP430x2xx family and peripherals are similar to MSP430G2553. 

Alternative to pull request #309, I independently developed the same thing :) However my version has the following differences:
* this one only includes boards.txt and pins_energia.h
* pin numbering according to silkscreen on PCB and schema in user guide (unlike 309)
* based on Energia fork from 3/16, i.e. uses new format for analog pin definition
* slightly different numbering for LED, debug serial etc.

Tested:
- Serial (9600)
- digital write to both LEDs
- digital read of push button
- analog read of temp sensor
- delay