planet_main.php: add space between Launch button and ship list
planet_main.php: add space between Launch button and ship list

The spacing likely changed when we converted the Launch button from a
form to a link in 79f11841d7.

hemberger/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr,smrealms/smr,smrealms/smr