Split in place

• added split in place; you can now either split a copy of a file (slower, requires more storage, but maintains original copy) or split in place ( faster, requires 4gb of storage, but deletes original copy)
• now allows a second file to be split after first one is done

not really proud of the code written here, but i feel it's better to release this and people to use it, than for me to keep it until I have time to clean it up... so crapy code it is 😄

v1.2

-fix this buffer write to disk
-added placeholder temp icons

Update minimum OS version

updated minimum required OS to support macOS Sierra 10.12

first test release

initial release of the SplitNSP-Swift-GUI