card string name consistency

[bowrango]

Need to ensure that decks contain valid strings for the keys in the card2idx map.

This will involve formatting the strings in a standard way.

Note that in the graph metadata within create_empty_graph(), the cards go by "name" and "key" attributes.

[bowrango]

• The card2idx map uses all lowercase with no spaces or other characters for the card names (e.g. xbow, knight, pekka).
• Each node attr dict in the graph has some different conventions (e.g. 'key', 'name', 'sc_key'). Removing dashes for the 'key' convention will match card2idx. This is preferred.
• In Client.build_graph(...), the deck lists have all special characters removed. Consistency here is important. This formatting should be done at the higher-level Client.get_top_decks().