Feature/mixpanel

Adds a basic settings file to include Mixpanel and adds the context processor to enable Mixpanel in the template. Override the MIXPANEL value in your local settings value and add the key to activate Mixpanel. For example, use MIXPANEL = "831248712"
The last enter is really needed here because testing deploy will append the commit hash here and it will be on the same line as MIXPANEL = ''.
Other that that it's coding standards to have an enter here ;-)

Sorry for being nitpicking :-o