Add Routes nextResult() and previousResult()

[DylanVanAssche]

1. What happens:

   • Loading more routes requires a new request to fetch all the routes between stops for a certain time range.
   • See Add Liveboard::Board nextResult() and previousResult() #62

2. What was expected:

   • Allow appending of current route searches

3. How to reproduce:

   1. N/A

4. Environment:

   • Sailfish OS version: 2.1.1.18
   • Sailfish OS hardware: Xperia X

[DylanVanAssche]

Extending earlier departure time, no problem, just do it!
Extending later arrival time, start from scratch!

[DylanVanAssche]

Depends on #77