All subroutine arguments should have an `intent`

[sbryngelson]

All subroutine argument variables in the entire code should have an intent.

For example, in the below, idir should have an intent(in): https://github.com/MFlowCode/MFC/blob/31aed98a45c010df5226bedefcc910f1b119c1f5/src/simulation/m_bubbles.fpp#L129

Options are intent(in), intent(out), and, if neither applies, intent(inout).

I wish I knew how to get the compiler to spit out warnings for this, but I'm unsure if there is a flag.

• [x] #477
• [x] #478
• [x] #479
• [x] #480

[sbryngelson]

completed with #477 #478 #480 #479 thanks @okBrian