Hold flash after restart mspsim

Read/Write to file

Only active when filename is set

Use cpu.setFlashFile to set a filename
Support MSP-EXP430F5438 board

Node for MSP-EXP430F5438 board
Watchdog Interval Timer Interrupt Bug

Watchdog Interval Timer call setBitIFG but interrupt is not flagged.
Workaround this by calling cpu.flagInterrupt(58, this, true);
PxSEL and PxSEL2 Support

Two variables (selValue,selValue2) are defined. This values represent
the inputs which are switched to output via PxSEL,PXSEL2. This values
must be set by timer, ccu, ad-convert,... via writePortSel

Disable set in to 0 after reset. Because this are inputs and the
physical connection to other components is not affected by the reset.
Timer and Watchdog improvments

Timer:
- correct calculation of next event when not running to 65535
- PxSEL/PxSEL2 support
- correct events in all modes (UP,UP/DOWN)

Watchdog:
- Support Watchdog of F5438 
     3Bit WDTISx (switch Watchdog type via version variable)
- update delay on register changes
Bugfix for Flash

Only info mem is read/written to file because firmware is overridden
when flash is written after reading firmware.

Small improvements in file handling