left sidebar should include menu options when meaningful and be optional as a whole

[panosnethood]

In version 2.5.4, I see the left sidebar in the portal page with 4 menu items, 2 of which ("sensors" and "monitoring") lead to empty pages and "system" is mostly uninteresting (in my opinion).

I would like to ask for two improvements:

• First, remove menu options when they don't contain information
• Make the whole left sidepanel optional. I really prefer that it is not there in the simplest scenario since users can always go to Applications just by pressing on the "home" button.