Fixing aria warnings in Chrome lighthouse related in issue #195

[juliano-nunes]

closes #195 + more additional fixes to get this lighthouse/spec compliant

aria-readonly attr on input has been removed - Not sure why it was added in the first place? According to w3 aria spec (http://w3c.github.io/html-aria/#index-aria-combobox) readonly and aria-readonly properties can't be used when role="combobox". This aria-readonly attr also shows an error in lighthouse aria validation.

remove initial empty aria-activedescendant (aria-activedescendant="") - This seems to go against the spec also (see w3c/aria#501 and validator/validator#557) and also shows an error in lighthouse aria validation.

add correct aria-owns id reference, and if no id is present on input, generate a guid from helpers and attach to menu - this fixes the issue outlined in #195, the previous change for this (line 45) never worked as it was referencing 'www.menu' which never exists, and even with the correct reference 'www.selectors.menu' also wouldn't have worked as it would've just changed all the menus ('.tt-menu') the the last input id that was initialised

This pull request is an copy of #197 created by @mattywong. His changes are totally ok, but his branch was merged with master branch and travis is broken, so I have create this branch to help solve this.