`Template` rework

[jurchiks]

• Template - if included/parent template cannot be found by $path alone, attempt to prefix dirname($this->path) from the initial template.
• Template - reorganize code - public/protected/private.
• Template - rewrite to restrict access to private variables from within the templates, OR separate the template composition from rendering entirely.
• Engine - rework to use Option for getTemplate()
• Engine - make callFunction() arguments optional
• Engine - optimize order of function search in callFunction()