Slim Query/Table Table: manage variables assignment in VariableStore

Variable set ($X=) was not possible on QueryTable(#91 and #369) and TableTable.

I have found a solution for TableTable (pull request #469) but it was not applicable on QueryTable.

This pull request propose a solution to manage both tables:
I have added a variables map in TestResult returned by expectation.
And do a new instruction 'assign' on SlimClient which set variables in the VariableStore.

This pull request requires a protocol modification, other implementations need to be updated (http://www.fitnesse.org/PlugIns#slim).
If the modification is not done in plugins, variables in theses tables can't be used.

// Assign the symbol using the echo function
// This will only work for strings
        	assertion= makeAssertion(callAndAssign(variable.getKey(), "scriptTable" + "Actor", "echo", variable.getValue()), new SymbolAssignmentExpectation(variable.getKey(), col, row)));
// Better Assign the symbol using a clone function and refrencing the original table structure
        	assertion= makeAssertion(callAndAssign(variable.getKey(), "scriptTable" + "Actor", "echo", "$SystemQueryResultSymbol", variable.getRow(),variable.getColumn()), new SymbolAssignmentExpectation(variable.getKey(), col, row)));