[Utils] List of possible filter_values would be helpful

[Rubix982]

It can be useful to tell the user what kind of filter_values are possible when dealing with filtering the value in `properties.

For example, in #1, we see filter_values as,

# list of values to filter for and keep -- update this if changing to traffic signs
filter_values = ['object--support--utility-pole','object--street-light']

But I was unable to find this list of filter_values in the API docs.

This is related to #27 as we can check if the filter values given are correct, and alert the user if they've passed in the wrong filter values, and even provide as the mechanism for help as discussed in the Discord Chat (I can't find the issue that was made for this?). This is similar to #48 , but in the context of a help function.

Help needed, @cbeddow

[cbeddow]

The official list for now is under "traffic signs" and "point" here (points == map features in this context): http://web.archive.org/web/20210105003120if_/https://www.mapillary.com/developer/api-documentation/#traffic-signs
http://web.archive.org/web/20210105003120if_/https://www.mapillary.com/developer/api-documentation/#points

This exact list should migrate to the new API docs soon but I cannot predict exactly when. Does this help for now? Maybe a text file is best to use with a fallback to scraping the website that we can switch to when these are live on the web?

[Rubix982]

I agree with the file idea, we can scrap it pretty easily and keep it for checking locally, then move to remote API checking when it's finished on the API's end.

[Rubix982]

This would need to be shifted to the documentation as well.

[eneerhut]

Traffic sign list.
Point feature list.