Updated inline config documentation

Added reference to trade header removal. This allows users to disable
the trade header at the top of the page by setting currency to an empty
string.

Addresses #305
Modfied templates to support empty trade currency

This will remove any template content related to the trade currency if
that one is left empty in the configuration.

While going through the templates I also cleaned up the PHP Warnings
left. The code and templates should now process without throwing any PHP
warnings.

Fixes #305 and further addresses #301
Merge pull request #306 from TheSerapher/issue-305

Issue 305