fix timing options

The timing options are checked first. The logic is the following:

• if a segment file is provided, it is downloaded
• if, additionally, a time range is provided, the segment list is intersected with that time range
• if no segment file is provided and a time range is provided, the time range is used as a single time segment.

The resulting segment list is checked and the effective range is updated

If no segment file is provided, a channel name and a time range must be provided. Standard omicron trigger files are identified with GetOmicronFilePattern().

Note that there can be no timing info if trigger files are provided. In that case trigger segments are used.

Closes #2 (closed)