Hot Keys Tab: display basic info for user

[antonkovalenko]

1. Write brief info above the table: Top keys contains a list of table primary key values that are accessed most often. Sample is collected upon request to the tab during 5s time interval. Samples column indicates how many requests to the particular key value were registered during collection phase.
2. brief info must be displayed in info block with control to close it forever

[adameat]

@adameat