Mseedindex

- Rework logic to track all conterminous records with the same NSLCQ
as a section regardless of time order, each section will be exactly
one row in the database.
- Add time span tracking for each contiguous NSLCQ section in file,
store as array of numrange values (epoch times) in 'timespans' field.
Data with a sample rate of zero is not included in the time span list.
- Remove tracking of segment count and gap seconds as these do not
work properly when data is not in time order.
- Set time index to NULL when the earliest data in a given section is
not represented in the index. It would not be usable to indentify
a contiguous read range including all data.

- Rename to mseedindex from mseedsyncdb.

- Store file modification time in new filemodtime field.
- Improve failure handling on memory allocation errors.

- Track time indexing within a segment at one hour intervals and
store indexing in a new hstore field.

- Update to new schema using separate network, station, location,
channel, quality as character fields instead of nslcq ltree.

- Group conterminuous NSLCQ records in a file and track number of
continuous segments and total gap (non-coverage) for each group.
- Update to new schema supporting the segment count and gap value.