Add Documenter features at the plant level

[fletchapin]

This is not an exhaustive list:

• Sed tank
• Flocculator
• CDC
• Entrance Tank
• Filter

[fletchapin]

There are a few plant-level docs I'm not sure where to include:

• Rapid Mix
• Construction Materials

We will always include an Appendix and Introduction, but the above sections are only relevant to certain parts

[oliver-leung]

TODO: Break this issue down into multiple issues, one for each plant component.

[fletchapin]

Split this up into #34 #35 #36 #37

Updated title and left it open to make sure of the following:

• Smart Component versions of LFOM and ET get Documenter features attached
• Rapid Mix and Construction Materials Documenter features are created at the plant level