Fix #464 - Support placeholder attribute for inputs in find mode

Whereas find mode normally identifies inputs by their value, if a value
is blank, find mode will use the placeholder value instead, if it exists
Merge pull request #748 from mhchen/issue_464

Fix #464 - Support placeholder attribute for inputs in find mode
Make smartcase locale-aware.
Fix #766 vomnibar is displaying incorrectly on pages that have CSS setting the input styles
Merge pull request #767 from neouser99/master

Fix #766