Update the translation functionality to always use the property files without a language code as the default translation

[dubdabasoduba]

Currently we have to always add a language code even on the default translation file. Research from other platforms shows the default property file having no language code e.g https://github.com/openmrs/openmrs-core/tree/master/api/src/main/resources & the strings on the android platform.

• [x] Translation functionality update to match the above description.

[cafootitt]

@dubdabasoduba Is this done and QA'ed?