Sign button text doesn't change to "already signed" for initiatives

1. When clicking over the "Sign" button in Initiatives the button changes color but it doesn't change text, the button changes from red to green, yet it says "sign". Participants not familiar with color-codes, when already signed, will see a green button saying "sign" and they will click it to sign, to see that it changes to red, without knowing what that means. 2. Together with a change of color the button text should change to "Already signed" when participants click on it. 3. I found this bug in meta.decidim.org initiatives. v. 0.15