DB: convert number to int in find_job

As we pass number around as an html parameter, this change will
explicitly convert the 'number' option to an int within
db.find_job.
WEB: number parameter now remember when using up button

Previously the web interface would not remember the number of
jobs the user had selected to display if using the pagination
links from within a job_info page. This commit essentially
treats the 'number' option much more like all the other job
query parameters, instead of handling it as a special case that
often doesn't get passed.