#5 Add a button to reset exception handler to <<SPIM Exception Handler>>

[Renaud PACALET]

Version: svn release 691 (2016-11-18 15:58:33 +0100)

After an alternate exception handler has been used, to come back to the default exception handler, users must enter the exact "<<SPIM Exception="" Handler="">>" string in the Simulator -> Settings -> MIPS -> File QLineEdit text box. This not that easy to remember. This patch adds a slightly more convenient "Default" button (right to the "..." button) that does this.