[#279] Fix: Invalid "Project" struct when initializing Elixir project with custom module name

What happened 👀

Update the Project struct to contain more accurate information about the project structure.
Add typespecs to the Project module

For the mix project, it needs to get the base module from the mix.exs file because the mix project does not have access to Mix.Phoenix.base/0
For the mix project, since the generated project does not have the structure same as the web project, so it does not have base_path and web-related path and modules. Therefore, all the fields related to that are set to nil

Project type	Project structure	`Project` struct
Mix project
Mix project with custom module
Web project
Web project with custom module