Move all hardcoded user displayable strings into a locale header file

[davetcc]

Going forward, no user-displayable text will be hard coded into a CPP file. Instead, each textual item will be broken out as a constant EG TXT_DIALOG_OK_TEXT, and the text behind the definition will be found in each of the locale header files.

There will be a header file language_select.h that will use the following priority logic to determine what to include

If header project_locale.h exists then that will be used first with absolute priority.
If TC_LOCALE_YourLanguage is not set, the English language header is included.
Otherwise, it will go through the remaining languages, again English is the default.

[davetcc]

I've tested with no locale (English) and French, works in both cases. This does not solve the problem of multi-language menu items, but it does put the base in place that will allow this in the future. We ask that anyone who can creates PRs with additional locale files for other languages.