#507 improving Expressions window

[reza]

for debugging project that has more than two modules checking variables' value is essential.
adding these items to expression window is necessary:
1-grouping variables list by file name (module)
2- user can customize the group name
3-adding folding (open and close ) variables groups
4-has a possibility to freeze some values calculation (only in expression window) : when number of defined variables in expression window is increased program debugs slowly