load PacBio data and perform sQTL analysis

[jsaquing]

additions:

• can load PacBio transcripts and exons from LRP pipeline output
  • PacBioTranscript has SQANTI classification (FSM, ISM, NIC, NNC) as an attribute
• PacBioTranscript and GencodeTranscript have a new many-to-one relationship indicating association between FSM/ISM transcripts and the reference transcript they match
• ExceptionLogger helper class for reporting exceptions w/o halting entire script
• IsoformPlot changes:
  • updated color schemes for different transcript types and pblock categories
  • isoform information can now be displayed in a table to the left of the plot
  • IsoformPlot can be drawn inside a subplot

refactoring:

• ORF objects are now constructed from CDS intervals in gtf file instead of transcript-relative intervals in fasta headers
• database loads from GENCODE comprehensive set
• database only loads genes designated protein_coding
• initialization of attributes in Protein class moved out of reconstructor methods and into cached properties

closes #71, #74