Rewritten the file to make it work with Redmine 4.2

[mgi1982]

This fixes the 500 you may get if you upgrade RM to 4.2.

[haru]

This PR fixes the conflicts with plugins which uses 'alias_method' funciton but makes new conflicts with plugins which uses 'prepend' function.
And you should use 'prepend' on Rails 5.
https://www.bigbinary.com/blog/rails-5-deprecates-alias-method-chain

[phlibi]

Are there any plans on integrating this patch or an improved one? We have recently added the checklists plugin of RedmineUP (https://www.redmineup.com/pages/plugins/checklists), which now causes the conflict when opening the project settings. I can confirm that the PR fixes the problem for at least this plugin combination. But using a more future-proof approach would certainly also be a good thing.

[haru]

Are there any plans on integrating this patch or an improved one?

No plans.
I think the checklists plugin should be fixed.