Separate block icon and title sizes. Update icons

[Manoj Solanki]

Currently there is only one setting for the block header font size which affects icon and actual content. Make this separate so font icons can be any size.

Also change default sizes for both of these. Update the default icons and default font used for block titles where possible to make them more modern.

[Manoj Solanki]

Fix #898. Also changed default for search box padding top.

→ <<cset d521ff1209dd>>