Chore: Load translations dynamically

[gmaclennan]

Current behavior:
Mapeo Mobile loads all language translations into memory on app start. As the number of translations increases this has a cost for app load time and has an impact on app memory usage. This is particularly important on low-end phones with limited memory: we want to keep Mapeo Mobile memory usage to an absolute minimum.

Desired behavior:
Load languages dynamically when the user changes language. Current use of require() bundles everything into a single JS bundle that is loaded at startup. I see two solutions:

1. Build translations into an asset folder, and load them dynamically with react-native-fs when the user changes language
2. Switch to RAM Bundles that will dynamically require modules at run-time. This adds complexity to the overall build, but could bring start-up improvements to the whole app