Search by Category and price, etc... for VIEW POSTED AD

[hlee2052]

• need to run npm install first
• if something does not work, try deleting old stuff in database (see my previous pull request for instruction)

1. updated UI for for view posted AD (UI for individual items should be an easy change later)
2. filter on left side
   • if category left blank, then queries every category
   • min/max is optional : you can input either none, one, or two numbers
3. Num items per page/pagination: takes eeffect after press submit (default: 5 items per page)

Query by string:

• I did not do this yet:
• search all character in description using regex, etc probably too costly and slow
• may be use index instead (eg, during post new item, user can specify a few keywords... turning every word in description in index may not be good...not sure...) https://stackoverflow.com/questions/13606555/how-to-perform-keyword-query-in-mongodb