fix #805 - recipients autocomplete

Fixes #805, #810, #840 and #890, all the same issue - autocomplete for recipients of a note or picture doesn't work when you start typing a name from beginning. The cause: API search query was mistakenly receiving a term converted to lowercase, but it is case sensitive, causing the query to fail for any capital letters, such as first letter of a name.

Alternative solution: queries could be case insensitive, so that user can type a name without paying attention to capital letters. But that is a design decision, this patch fixes the issue.