Add PCA grading support

PCA is a European card grading service that is gaining recognition, especially in the Pokémon TCG market. Adding support for PCA grading would expand PriceCharting's graded data offerings beyond services like PSA and BGS, catering to a wider user base, particularly those in Europe. This broader inclusion would provide more comprehensive and diverse market data, leading to a more complete and accurate picture of collectible values. Ultimately, supporting PCA grading would enhance PriceCharting's authority and utility for a larger international collecting community.