Enhancement: Automatically detect file/curl method for XML API

Added automatic detection for whether to use cURL or file method for
querying the XML API in Pheal.
Enhancement: Expanded ACP Troubleshooting section

Added the following checks to ACP -> Troubleshooting:
- check for cURL availability
- print full qualified path to API caching folder
- check existence of API caching folder
- check whether API caching folder is writable
- check API connection (converts a character ID to name for testing)
- check public CREST connection (fetches a sample kill from CREST)

- print full qualified path to SQL query caching folder
- check existence of SQL query caching folder
- check whether SQL query caching folder is writable

- print full qualified path to Object caching folder
- check existence of Object caching folder
- check whether Object caching folder is writable