Add layer in navstack

[Travellerer]

• [ ] xml
• [ ] layers: (Static layer, obstacle layer and inflation layer already used)
• [ ] a) Valley layer: Keep Bot near graph path
• [ ] (b) Intention layer: Add costs for space robot is moving to very next)
• [ ] (c) Crossing layer: Add costs on one side of moving obstacles to always pass on one side.)
• [ ] normalize costs (in case they exceed the max range) #15
• [ ] gaussian function
• [ ] initialization functions
• [ ] updateCosts functions
• [ ] find/check for possibly error-creating situations to test on later