Feature execute code

[sir-onze]

In sequence of the article's future work and Issue #1 this PR implements the ability to run code written in the web expressions editor. The development was done using antlr4 visitors, an initial traverse is done to collect the input variables and a second to calculate the expressions values.

It is now possible:

• Assign values for each variable written in the input section via a modal (only numeric values);
• Execute and calculate the expressions based on the inputs and operations;
• Visualize the results in a section below the editor;
• Visualize errors regarding operations (division by zero);
• Visualize errors related to the use of not defined variables;

Added tests to cover the new visitors implementation.