consistent docs with entity renaming

[koehlerson]

with #914 some docs are off

• https://github.com/Ferrite-FEM/Ferrite.jl/blob/master/src/Grid/grid.jl#L281-L308
  Solved in Document reference shape entity naming #935
• https://github.com/Ferrite-FEM/Ferrite.jl/blob/master/docs/src/topics/grid.md
  Solved in grid.jl docstrings and remove qualified Ferrite names #933
• https://github.com/Ferrite-FEM/Ferrite.jl/blob/master/docs/src/topics/boundary_conditions.md#L101
  Solved in Document reference shape entity naming #935

maybe more, feel free to add items to the list

[KnutAM]

Thanks, I'll start adressing these now that the mesh parsers have fixes!
Great if anyone who finds inconsistencies add them here!