History log overhaul and giant-map optimizations

The history log panel has been rebuilt so you can jump to any year and turn pages forward or backward with precision.

Improvements:

• Heightmap and biome painting on huge maps now runs much smoother, eliminating the heavy stutter that used to happen after finishing a pass.

• Sea routes render faster by merging their meshes to cut draw calls.

Bug fixes:

• Fixed some provinces inheriting tiles from neighboring provinces after generation.

• Fixed rebel wars continuously spawning new armies.

• Fixed the family tree panel occasionally opening with no characters.

• Fixed national borders failing to refresh after rivers were cleared.

• Fixed the Translate Map command under Map Editing -> Global Commands so it now completes successfully.