Fix template render when have no sidebar

Change the initialization of sidebar and navbar,
the way it was coded there's no way to override settings during the
tests since the Sidebar and Navbar are both loaded when the file
is read.

Rewrote the tests and added a new test to check if template
is corrected rendered when no sidebar is defined
Merge pull request #4 from raphapassini/fix-empty-sidebar

Fix empty sidebar