Improving Core interface

[kkiani]

Damavand has come a long way since the beginning of the project. Some of the names and designs of the core/base classes and methods were originally based on ideas that are now either deprecated or have been replaced. This issue lists a set of small improvements and enhancements to the naming conventions and interfaces of Damavand's base/core classes to make them more intuitive:

• Changing extra_args property on base controller to keyword_args to follow industry standard.
• Changing the name of ApplicationController class to BaseController to prevent confusion.
• Removing imports in the __init__.py files to prevent importing all features when importing one.
• Replacing the use of @cache and @property decorators together with @cached_property.