Refactor logging and some things more

Hi,

I have just refactored some annoying things mainly in the logging mechanism.

-     Refactored Logging mechanism
-    Add config flag to enable or disable API call logging (as this fills unnecessary the log file) Default State: disabled
-    Change class name to factory name core/template
-    Removed name 'zendesk.log' to replace it with the log constant
-    Refactored getLogSize() as this throws an error when the file not exists.
-    Removed hardcoded adminhtml route
-    Removed hardcoded adminhtml route, in getUrl
-    Removed unneeded method getFormHtml()

Would be nice if it can be merged in time.
Any other suggestions appreciated.

Thanks!