Convert "layer" argument to "layer_id" in Shiny functions

[mhpob]

Response to #86.

There are a bunch of misc. Air formatting changes in there (sorry!), so here are the pertinent changes for your review:

• Convert layer argument to layer_id and add dots (incl. to roxygen comments)
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L160
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L225
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L451
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L510
• If layer_id is missing, check for layer argument in dots. For compatibility with code written in previous versions where the argument was explicitly used.
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L162
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L227
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L453
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L512
• Change misc. layer = layer to layer = layer_id
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L180
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L197
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L207
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L227
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L262
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L272
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L471
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L487
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L535
  • https://github.com/mhpob/mapgl/blob/e96a53166d86dc916e4b22d8547b7e27f8ecf238/R/shiny.R#L551

[mhpob]

@walkerke I'm opening this PR in draft as this line also contains a reference to "layer = layer". I'm unsure if this is referring to underlying JS (don't change) or the object (should probably change). If you could give me direction on this, I'll tie it up and submit the PR.

[walkerke]

@mhpob in that example, we are referring to the layer specifically as we add it to the map - so we won't want to change that / can leave that function untouched.

[walkerke]

We ended up doing some edits that introduced a bunch of merge conflicts, so I ended up handling separately to streamline. I do appreciate the contribution though!