Collapse white-spaces in keyword_lowercase analyzer

[lukas-vlcek]

We are using keyword_lowercase analyzer in couple of places (for example on sys_tags). This means the search requires exact match up to lower/upper cases. In addition to this it meight be useful to collapse all white spaces during the analysis to allow match in cases like:

`bpm suite` vs. `bpm   suite`
    ^               ^^^

keyword_lowercase is defined here: https://github.com/searchisko/searchisko/blob/master/configuration/index_templates/defaults.json

May be we could use pattern capture token filter to collapse multiple white-spaces to a single white-space?