Add tooltip for bookmark warning.
Add tooltip for bookmark warning.

ucscXena/ucsc-xena-client,ucscXena/ucsc-xena-client,acthp/ucsc-xena-client,ucscXena/ucsc-xena-client,acthp/ucsc-xena-client,ucscXena/ucsc-xena-client,ucscXena/ucsc-xena-client,acthp/ucsc-xena-client