WebStat: add modifications and fix errors

• The returns graph crashed because the due_date value of some loans was not set. It is fixed now
• The returns value in the yearly report was the same as the loans value in the yearly report. It now shows the correct returns value
• Average time between the date of the record creation and the date of the first loan was not well calculated in the loan statistics. Now it shows the correct value and displays the measurement unit (days)
• In the CERN site, use only the items in the "Book & Proceedings" collection for the loan statistics
• Remove user address filters
• Fix custom query summary (use CFG_JOURNAL_TAG variable)
• Add urls to custom query summary
• Add id to ILL requests list
• Fix select date crash (strptime method is new in python version 2.5, changed to the old way)
• Add loans lists limit
• Fix ILL requests statistics
• Show SQL query in key statistics and refactor
• Add truncated udc values
• Change 3 months to 2 weeks for ILL requests
• Add CFG_WEBSTAT_BIBCIRCULATION_START_YEAR to limit stats
• Add full lists
• Fix loan lists queries. They now return values in a reasonable amount of time
• Improve page load times
• Fix error log analyzer search string
• Improve collection stats
• Improve documentation
• Add new records stat