Limit the Experimenter/Group names in combobox to 25 chars

This fixes the problem that the SearchPanel gets very wide if there
are groups and/or experimenters with very long names
Limit the number of search results returned by the OmeroDataService

This fixes a problem, that the search in Insight appears to hang
on very large searches (e. g. date range only search); also prevents
OOM exceptions as the size of search result table also is limited
this way.
Made use of the EditorUtil.truncate method