Set value to decompiled variable

[Escapingbug]

With pcode patch implemented, now we can set the value to the variable by setting the variable varnode to specific value (i.e, patch a COPY pcode instruction to that varnode).

The expected result of this is:

• Right click on a variable in the decompiler panel.
• In the context menu, select "set value"
• Popup a window, accept the value to be set
• alert the user about the to-be-patched instruction addresses
• When user click confirm, patch the pcode by prepending a COPY instruction.

Apart from those above, a "reset function pcode" function should be added. And a highlight (or other color) should be used to the patched pcode.