show the wildcard query suggestions

* show query suggestions
* make them clickable
* minor improvements to error messages
Merge pull request #4071 from dmwm/wildcard_multi_choice

show the wildcard query suggestions
Remove duplicate functionality of _dbs_inst with _instance in DASQuery class; it prevents from wrong qhash generation
some pylint and pep8 fixes

* now all files in keywordsearch package and kws_tests get >=9 in pylint
* most TODOs removed
* still some code may be cleaned up further