Updating BCs Documentation

[csdechant]

This PR is part of a continuing effort update the Zapdos documentation. In particular, this PR focuses on the documentation for the Boundary Conditions (BC) objects.

[csdechant]

Just a reminder for our email conversation, I haven't fully proofread the documentation, so please excuse any typos/left over self-notes.

[moosebuild]

Job Documentation on df3868b wanted to post the following:

View the site here

This comment will be updated on new commits.

[moosebuild]

Job Documentation, step Sync to remote on b302c5e wanted to post the following:

View the site here

This comment will be updated on new commits.

[moosebuild]

Job Precheck, step Clang format on 77376df wanted to post the following:

Your code requires style changes.

A patch was auto generated and copied here
You can directly apply the patch by running, in the top level of your repository:

curl -s https://mooseframework.inl.gov/zapdos/docs/PRs/250/clang_format/style.patch | git apply -v

Alternatively, with your repository up to date and in the top level of your repository:

git clang-format d16eeb0d73e664e51210f4017a757e46a96b0c85

[csdechant]

@gsgall @cticenhour This PR is ready for another review. There are some unresolved conversations that focuses on formatting, but nothing too big.