Host Biome's plague system

[Luligabi1]

After in-game Day 100, the Host Grass will start spreading towards another blocks nearby, slowly corrupting the neighbor biomes. The player must take action to stop the spreading of the plague, as it slowly kills animals and griefs buildings.

• [x] Basic spreading mechanism with different graphics when the Host Grass has been "disabled";
• [x] Vivifica Glyph to stop nearby spreading;
• [x] Morbus Glyph to allow nearby spreading (must be deactivatable);
• [x] Configurable count of days to start spreading.
• [x] Integrated, in-game way to see if feature is enabled/how many days to start spreading
• [x] Heart of Vivifica - Disables spreading.
• [x] Heart of Morbus - Re-enables spreading.
• [x] Morbus Grass, Tall Grass, etc.
• [x] Guide book page

[Luligabi1]

Most stuff for 0.5.0-BETA is done, but I'll keep this open as new problems and implementations surge.