Add a request router

[MauricioFauth]

This pull request introduces a router to help with the request management.

For example, we can use http://localhost/index.php?route=/server/databases instead of use http://localhost/server_databases.php.

The objective is to reduce the number of entry points and to use the index.php as a front controller redirecting all the requests to it.

The idea of using the route parameter is to help with the transition, as it does not require URL rewriting, however, once the transition is complete, it will be possible to use URL rewrite to have pretty URLs like: http://localhost/server/databases.

Other objective is to fix the issue that happens when opening some links in a new window, by creating unique routes without the problem of having an SQL query in the URL.

For now, it only maps 1:1 the entry points with the routes.
For example: /server/databases => server_databases.php

Once this is done, the next step will be to improve the routes by refactoring the libraries/entry_points files and adding more routes.

[codecov]

Codecov Report

Merging #15377 into master will decrease coverage by 0.01%.
The diff coverage is 15%.

@@             Coverage Diff              @@
##             master   #15377      +/-   ##
============================================
- Coverage     52.99%   52.98%   -0.02%     
  Complexity    14047    14047              
============================================
  Files           481      481              
  Lines         62011    62027      +16     
============================================
  Hits          32862    32862              
- Misses        29149    29165      +16

[codecov]

Codecov Report

Merging #15377 into master will decrease coverage by 0.01%.
The diff coverage is 22.52%.

@@             Coverage Diff              @@
##             master   #15377      +/-   ##
============================================
- Coverage     52.99%   52.97%   -0.02%     
- Complexity    14047    14051       +4     
============================================
  Files           481      482       +1     
  Lines         62011    62043      +32     
============================================
+ Hits          32862    32867       +5     
- Misses        29149    29176      +27