v0.1.0 beta release 2

v0.1.0
Second beta

Main menu:

• Added logo
• Added help screen
• Added level creation menu to input size
• Added settings screen

Level UI:

• Space key to start simulation
• Also fixed to make the play button not only make one step, but play constantly
• Set selected hotbar cell using 1-9 keys
• Go to next/previous hotbar item with (Shift+)Tab
• Combined rotators and push/slide cell
  Switch between them using the < key
• Reset with T or button in menu

Select tool:

• Move selection with arrow keys
• Rotate grabbed selection with Q and E
• Flip grabbed selection with R and F
• Fill selection with G (Shift+G for placables)

Extensions:

• Everything is extension-based now
• Added a music cell
• Added disabler cell
• Added orientator cell
• Added arrow cell
• Concept of "tools"
  currently auto can opener

Internal:

• Added slots (currently used for rotators and push/slide cell)
• Introduced a "cell type" system
• Reorganize UI files
• Unused error type for V2 code removed
• Updated window title to not be "Hello World!"
• Offset is now a Position