Add ability to analyze light chains

[marcelm]

Originally reported by: Marcel Martin (Bitbucket: marcelm, GitHub: marcelm)

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The light chain doesn’t contain a D gene, but the pipeline currently complains if there is no D gene database.

Other fixes may also be necessary. Perhaps the CDR3 regex needs to be modified.

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• Bitbucket: https://bitbucket.org/igdiscover/igdiscover/issue/3

[marcelm]

Original comment by Marcel Martin (Bitbucket: marcelm, GitHub: marcelm):

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It seems IgBLAST always wants a D gene database, at least the web interface does. This allows one to give it a mixture of sequences from heavy and light chains and it then decides for each sequence individually what it is.

[marcelm]

Original comment by Marcel Martin (Bitbucket: marcelm, GitHub: marcelm):

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This is working now.