fix: add method_exists check before calling method and replace security with encryption

In this commit, added an existence check before calling the checkEditPermission method in ajax files. The Security class use in some files was replaced by Encryption. This commit also made adjustment on getUser function to either return user object or null.

Related: #4 (closed)

mentioned in commit a774c06d

merged

This MR is included in version 2.0.0

The release is available on GitLab release.

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