[feature] Escape special characters when searching for contributors

From CenterForOpenScience/osf#1250 hopefully I've done the right thing!

**Purpose**
If you put quotes when searching for contributors, it returns A LOT OF results (that is, including those results that are not related to the search query)

**Cause**
Special characters are not html escaped properly, causing confusions whether they are parts of the search query or belong to lucene search syntax

**Changes**
Uses <code>re.escape(item)</code> to escape every special character in the query, except whitespaces. <code>item</code> do not contain whitespaces, since it is any element in the list "<code>items</code>" that is returned by splitting the query by whitespaces.