- In TerminalEmulator, interpret sixel sequences, and send them to
  TerminalBuffer for constructing a bitmap.
- Sixel sequences may be longer than 8192 characters, so break them in
  natural places ($,-,#), rather than collecting all in the buffer.
- The bitmap is sliced to character cell sized slices, and each the
  the style attribute is used to store which bitmap slice is displayed
  in place of this character.
- In TerminalRenderer the style is interpreted, and drawn using
  drawBitmap, instead of drawText.

Support iTerm inline image protocol (OSC 1337):

- Using the same bitmap display infrastructure introduced for sixels.
- Collects the image data outside of the OSC buffer.
- Ignoring some parameters.

Small emulator changes:

- Also eat APC sequences, not echoing to screen.
- Fix `CSI 14 t` to give actual size
- Add `CSI 16 t`
- Add `4` (sixel) to device attributes

Add missing {} that change the logic.

- For iterm2 images - catch the error, and cancel the image.
- For sixels - if it happens when resizing the bitmap, than ignore drawing
  outside of the current image.

- Move working bitmap code (drawing current bitmap) to
  WorkingTerminalBitmap class.
- Move bitmap handling code to TerminalBitmap class.

To avoid removing elements from the map while iterating over it.
This should solve the Concurrent Modification Exception in the bitmap
garbage collection.

Avoid crash when BitmapFactory cannot decode image

…last column.

This creates a zero length text run, so skip it.