Message log should keep out of the way

[michaeltwofish]

When a message is sent to humanMsg and the message log appears at the bottom of the screen, the #humanMsgLog div can invisibly cover other UI elements. For example, on the publish page, the save and publish buttons are not clickable if they're at the bottom of the window.

Only the tab itself should be clickable, and other elements at the same level should still be accessible.

[ddebernardy]

see also #601

[ddebernardy]

see also #1104