Started work on laying out the glyphs so they can be arranged in a grid

|SOURCE|
[FontWidget]
* Added member variables for padding, and the texture's width and height
* Added width and height parameters to the constructor
* When the current X position exceeds the width of the texture, the X position
  is reset and Y is advanced by the maximum height discovered from the previous
  line of glyphs
[MainWindow]
* Passing 256x256 as the texture dimension parameters for the font