Treat data partition special

[NicoHood]

• If the item has "data partition" in it, do not allow it to be installed alone. Closes #103
• If the first partition is not a FAT partition or not bootable in json, treat it as not bootable. Do not show it in the boot menu, and do not write config.txt to it. Closes #102

Also fixes: #205

Adapted from 843059136100b780d73407e571aee0083deb2722 https://github.com/raspberrypi/noobs/commit/843059136100b780d73407e571aee0083deb2722#diff-7bd3a48ac1bcbb236a941bd9c1b24587

Tested:

• You can only proceed the installation if a non data partition was selected.
• Edit is not highlighted anymore over the data partition.

Please have a look at the 2 commit separate. The first does the fix, the 2nd just indents code.