Implement wildcard queries with N

[sdelatorrep]

In the spec (see here), we can read:

    ReferenceBases:
      description: |
        Reference bases for this variant (starting from `start`). 
        Accepted values: [ACGTN]*. N is a wildcard, that denotes the 
        position of any base, and can be used as a standalone base of any 
        type or within a partially known sequence. For example a sequence 
        where the first and last bases are known, but the middle portion can 
        exhibit countless variations of [ACGT], or the bases are unknown: 
        ANNT the Ns can take take any form of [ACGT], which makes both ACCT 
        and ATGT (or any other combination) viable sequences.
      type: string
      pattern: '^([ACGTN]+)$'
    AlternateBases:
      description: |
        The bases that appear instead of the reference bases. Accepted 
        values: [ACGTN]*. N is a wildcard, that denotes the position of any 
        base, and can be used as a standalone base of any type or within a 
        partially known sequence. For example a sequence where the first and 
        last bases are known, but the middle portion can exhibit countless 
        variations of [ACGT], or the bases are unknown: ANNT the Ns can take 
        take any form of [ACGT], which makes both ACCT and ATGT (or any 
        other combination) viable sequences.
        
        Categorical variant queries, e.g. such *not* being represented through 
        sequence & position,  make use of the `variantType` parameter.
        
        Optional: either `alternateBases` or `variantType` is required.
      type: string
      pattern: '^([ACGTN]+)$'

Implement this usage of N as a wildcard for [ACGT] in both referenceBases and alternateBases parameters.