Configurable Nether Portals

Adds 5 new gamerules:

| Description | Description | Description | |-|-|-| | `portalsAllowCryingObsidian` | `true` | Whether portals can be created using crying obsidian. | | `portalsAllowCustomShapes` | `true` | Whether portals can have non-rectangular shapes. | | `portalsCustomSearchMaxDepth` | `512` | How many blocks will be searched for a valid portal, before giving up. Only used if `portalsAllowCustomShapes` is `true`. | | `portalsCustomShapeMinBlocks` | `1` | The minimum number of portal blocks needed to be a valid portal. Only used if `portalsAllowCustomShapes` is `true`. | | `portalsCustomShapeMaxBlocks` | `512` | The maximum number of portal blocks needed to be a valid portal. Only used if `portalsAllowCustomShapes` is `true`. |