Fix for loading user config file

[Karandra]

Fix for SettingStore::LoadUserSettings. Uses plugin file name as modName for ReadINI function instead of use INI file name.

Some user reported that MCM doesn't read used config file when name of the config file doesn't exactly
match to name of plugin file. That is, when file names differ only in character case, MCM will not read user config. Proposed change searches for all plugin files and if there is user config file for this plugin, calls SettingStore::ReadINI with plugin file name as modName argument to ReadINI and not with user INI file.

New loader code is written using some C++17 features, but can be easily rewritten to compile with older versions.

Sorry, seems like GitHub converted line endings in .cpp file.

[Karandra]

Seems like your AppVeyor don't support C++17.

[Karandra]

I've changed search location from Data folder using plugin file name to Data\MCM\Config using mod folder name as modName. This way modName should match the name defined in config.json file even if plugin file name doesn't.

However, there are some mods that breaks the rule "folder name (in Data\MCM\Config)" should match the name defined in config.json, "FO4 Difficulty Setting" for example. Though FO4 Difficulty Setting doesn't use MCM config file to store its config so that's not an really an issue for this mod.

[Karandra]

Changed SettingStore::m_settingStore hasher and comparison to be case-insensitive, also m_settingStore now stores Setting object as std::unique_ptr and not as raw pointer to avoid memory leak in SettingStore::RegisterModSetting on replacing existing setting with new one (line 281).

You may need to manually add StringUtil.h file to the VS project because commit doesn't include changed .vcxproj file.