Some fixes

resolves #13
resolves #14
resolves #15

# Changelog

#### Creating themes
* theme name length limited to 30 characters

#### Theme URL
* theme URL is not displayed if it's set to null
* theme URL is displayed in separate line

#### Plot models
* it's now possible to set points of a model via command

#### Terrain generation
* fixed sandstone type for paths
* theme name is split in 2 lines on sign if longer than 15 characters

#### Other
* players can teleport to their plots
* players can reset their plots
* added tools to place water, lava and fire