[2.2, UI] Action errors are inconsistent

[Maria Vrachni]

[2.2.0rc2, UI, Machine actions] The action errors need improvement on wording and presentation.

Bug description:

* Current result:

Given I have taken an action that returns an error
When I read the error
Then I see symbols like /, {, } and I have to read carefully to understand what the error is

* Expected/ correct result:

Given I have taken an action that returns an error
When I read the error
Then the error should be phrased in a clear way and shouldn't contain symbols that don't serve a purpose.

[OS X Sierra]

Chrome, 56.0.2924.87 (64-bit)

[Steve Rydz (steverydz)]

I think for this we'd need a consistent format for errors from the backend. Sometimes it's a string, sometimes it's an object and the keys in that object can be different depending on the error.