ISSUE-218 data_position.lon needs to be cast to integer in tagbase_materialized_views.sql

[lewismc]

Addresses #218 I observed that although all 4 materialized views (mview_vis_data, mview_vis_data_histogram, mview_vis_data_profile and mview_vis_metadata) were created only mview_vis_metadata was actually populated. We need to do more testing on the generation logic.