Set up a website with documentation based on the MooseDocs system

[smpark7]

We currently rely on Doxygen for Moltres' documentation on https://arfc.github.io/moltres/. Ideally, the documentation should contain helpful information about the input parameters of each class and sample input files showing how they're used.

While Doxygen documentation provides useful information on class inheritance trees, functions, and attributes, it does not provide any information on the input parameters of each class because MOOSE handles input parameters through instantiations of InputParameters.

The MooseDocs system is a potential solution as it provides a framework for generating a customizable website and documentation for classes as shown in here. MOOSE uses this system for their main website. Instructions for setting it up can be found here.

This issue can be closed when a website is set up for Moltres. The website should at minimum include a homepage, a MooseDocs documentation page, and a Doxygen page, with proper links set up for user-friendliness.

[smpark7]

With the initial setup implemented in #181, the remaining tasks are:

• Deploying the website to be accessible online (addressed in PR Set up new website built on MooseDocs system #199)
• Adding a link to our existing Doxygen-built website, or incorporating the Doxygen webpages directly into the website (addressed in PR Set up new website built on MooseDocs system #199)
• Filling up the following webpages
  • Contributing
  • Publications
• Migrate existing Moltres webpages in arfc.github.io into this website
• Filling up the documentation "stubs". Running the commands above automatically generates these "stubs" that contain information on the input parameters of each class. We should strive to include more information on the respective physics that each class models and examples of how they're to be used.