Add nexus.data.* function to manipulate saving data and move nexus.utility.

[NEW] Add nexus.data.* functions.
[MOD] Rename nexus.utility.getGameVersion() to
nexus.core.getGameVersion().
[MOD] Rename nexus.utility.getVersionString() to
nexus.core.getVersionString().
[MOD] Rename nexus.utility.upgradeGameData() to
nexus.core.upgradeGameData().
[MOD] Rename nexus.utility.registerDataUpgrader() to
nexus.core.registerDataUpgrader().
Move the setup data to data/scripts/setup.lua file.

[MOD] Move the setup data to data/scripts/setup.lua file.
[MOD] Change the error function in conf.lua to prevent crash when error
occurs.
Correct the wrong name in nexus.window.command.

[FIX] Correct the wrong name in nexus.window.command.
Add new nexus.window.common to draw general interfaces.

[NEW] Add nexus.window.common to draw general interface components.
[NEW] Add nexus.database.loadDatabaseData().
[NEW] Add nexus.database.loadExtraData().