Add external_data column to protein_feature and dna_align_feature tables, primarily for storage of user-uploaded data.

current ensembl/sql/table.sql.

not just "%_core_51".

Using this code on databases not patched up to the v51 schema will fail.

A pre-merge tag was put in place just before this merge:

  pre-multispecies-merge (in ensembl/modules/Bio/EnsEMBL)

cache than "$adaptor->{'_slice_feature_cache'} = ();" in user code.

tested 2 new methods: to get db_name for an external_db_id and fetch db_entries for a source (db_name)

added use of method bind_param_generic_fetch to allow binding parameters when using the generic fetch method

Correct the name of patch 'c' (meta --> meta_coord).

Adjust the insertion of patch identifiers to take into account the
species_id column in the meta table (needs explicit NULL).

added new method: bind_param_generic_fetch to allow binding parameters instead of using parameters within sql

Incorporated changes from patch_50_51_a.sql (version changes) and patch_50_51_b.sql (protein feature hit_id -> hit_name)