`lncdSql.visit_files(vid)`: collect files for visit_task

[WillForan]

needed for #33.
lncdSql should have two more functions
visit_files(self,vid) and task_files(self,vtid)

1. visit_files collects each task in checkedin visit that also has non null task.file. calls task_files for each. returns dictionary {'task1': task_files output, 'task2': ...}
2. task_files files for each visit task. return {'expect': number, 'files': {'file1_id' 'file1_loc','file2_id':,...
3. compare to task.files for count of files. if count matches visit_task.files, return contents of visit_task.files and expected count
4. search for files matching pattern of task.files. update db if any are found. return