message: [sql lab] improve placeholder strings for query search form
diff: @@ -183,6 +183,7 @@ class QuerySearch extends React.PureComponent {
  mutator={this.userMutator}
  value={this.state.userId}
  onChange={this.changeUser}
  + placeholder={t('Filter by user')}
  />
  </div>
  <div className="col-sm-2">
  @@ -191,6 +192,7 @@ class QuerySearch extends React.PureComponent {
  dataEndpoint="/databaseasync/api/read?_flt_0_expose_in_sqllab=1"
  value={this.state.databaseId}
  mutator={this.dbMutator}
  + placeholder={t('Filter by database')}
  />
  </div>
  <div className="col-sm-4">
  @@ -199,7 +201,7 @@ class QuerySearch extends React.PureComponent {
  onChange={this.changeSearch}
  onKeyDown={this.onKeyDown}
  className="form-control input-sm"
  - placeholder={t('Search Results')}
  + placeholder={t('Query search string')}
  />
  </div>
  <div className="col-sm-4 search-date-filter-container">
  @@ -226,7 +228,7 @@ class QuerySearch extends React.PureComponent {
  <Select
  name="select-status"
  - placeholder={t('[Query Status]')}
  + placeholder={t('Filter by status')}
  options={Object.keys(STATUS_OPTIONS).map(s => ({ value: s, label: s }))}
  value={this.state.status}
  isLoading={false}
  