[elm] Add support for Elm 0.19

[eriktim]

PR checklist

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Description of the PR

Add support for Elm 0.19. An option elmVersion is added to set the desired Elm version (defaults to 0.19). @wing328 can you handle the CI stuff via #878? I already added the Elm 0.19 binary to Shippable.

After this PR gets merged I will work on some other open Elm issues.

[wing328]

I've pushed a commit with minor enhancements and adding Elm 0.18, 0.19 to CI (travis, shippable)

Shippable (elm 0.19) reports the following errors:

Success! Compiled 1 module.
Compiling src/Request/Store.elm
-- NAMING ERROR ------------------------------------------ src/Request/Store.elm

I cannot find a `toString` variable:

61|     , url = basePath ++ "/store/order/" ++ toString orderId
                                               ^^^^^^^^
These names seem close though:

    List.any
    List.range
    asin
    ceiling

Hint: Read <https://elm-lang.org/0.19.0/imports> to see how `import`
declarations work in Elm.

[==================================================] - 1 / 1
                                                                     
Detected errors in 1 module.
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (bundle-test) on project ElmClientTests: Command execution failed.: Process exited with an error: 1 (Exit value: 1) -> [Help 1]

[wing328]

UPDATE: Travis (elm 0.18) reports the following errors:

Compiling src/Data/Order_.elm
Success! Compiled 2 modules.
Successfully generated /dev/null
Compiling src/Data/Pet.elm
-- TYPE MISMATCH ---------------------------------------------- src/Data/Pet.elm
The argument to function `list` is causing a mismatch.
61|                                                   Encode.list tagEncoder)
                                                                  ^^^^^^^^^^
Function `list` is expecting the argument to be:
    List ?
But it is:
    Tag -> ?
Hint: It looks like a function needs 1 more argument.
-- TYPE MISMATCH ---------------------------------------------- src/Data/Pet.elm
The 1st argument to function `list` is causing a mismatch.
60|                           Encode.list Encode.string) model.photoUrls 
                                          ^^^^^^^^^^^^^
Detected errors in 1 module.
Function `list` is expecting the 1st argument to be:
    List ?
But it is:
    String -> ?
Hint: It looks like a function needs 1 more argument.
-- TYPE MISMATCH ---------------------------------------------- src/Data/Pet.elm
Function `list` is expecting 1 argument, but was given 2.
60|                           Encode.list Encode.string) model.photoUrls 
                                                         ^^^^^^^^^^^^^^^
Maybe you forgot some parentheses? Or a comma?

[eriktim]

Thanks @wing328! Will fix the errors.

[wing328]

@trenneman all tests passed. Thanks for the enhancement!

[wing328]

Upgrade Note

Elm version defaults 0.19. To use 0.18, please set elmVersion:

--additional-properties elmVersion=0.18