Allow storage to be unlocked through SSH

Add ssh_authorized_key="<my SSH public key>" to cmdline.txt to activate SSH.
Add dosfsck

For folks managing to corrupt their FAT partition.
Send ATA trim commands by default during mkfs.ext4

Was previously turned off as it gave issues on some SD cards,
but seems to work ok now.
Add "netconfig" boot option to force displaying network settings dialog

For deployments that are meant to be used with static network configurations.
Make shutdown button less intrusive
Fix disabling buttons after delete

Closes #106
Select currently in use interface in network settings dialog

Closes #56