Add validation to the memory settings window.
Should assert:
- `max` memory is within (`initial`+`earlyGen`) ... `ceiling`
- `initial`, `earlyGen` >= Java's 64mb minimum
- `initial` > `earlyGen` (see below)
- values are numbers
Setting `earlyGen` equal to or higher than `initial` memory causes the game to crash with the following message -- which is not displayed to the user through either the launcher's output or its logging:
> Error occurred during initialization of VM
> Too small initial heap for new size specified