Adds way_type filter overpass query option to download non-highway da…

[hs-ye]

Adds two related but independent features relating to manipulating overpass query strings, that gives users the ability to customise the type of network they want to download using the down:

• Ability to select the way type in the overpass query e.g. Rail, instead of always downloading highways, which was harded in the constant WAY_FILTERS_QUERY
• Ability to pass in a manual set of filters for the overpass query (in a Dict), rather than having to choose from the fixed set as defined by the constant WAY_EXCLUSION_FILTERS

Defaults have been set for the new interfaces, so should be fully backwards compatible.

[hs-ye]

it uses the defaults maxspeed/reverseway from roads (which aren't actualy used in railways) at the moment, but i think the logic needs a major revamp around these functions in the graph_from_object function in graph.jl, to have proper handlers for different type of ways.

Note that oneway tag is actually in use in some parts for railways, have done a cursory check. But mostly i think it's assumed that railways do not have 'one ways' marked on the tracks the ways that roads do, even though by convention some tracks are going in certain directions.

add_node_and_edge_mappings!(g)
add_weights!(g, weight_type)
add_graph!(g, graph_type)
trim_to_largest_connected_component!(g, weight_type, graph_type)
add_node_tags!(g)

[hs-ye]

Todo:

• Split out the manual filter dict for power user feature to a separate PR, re-implement using muti-dispatch
• Merge the functionality provided by way_type into the network_type option, i.e. add a new constant for :railway for users to download only the railways
• Restrictions can be kept as is, with the default for rail being :none