Perfomance improvements which were made for EPiServer 7.1.3 are not in 7.6

Steps to reproduce

The fixes of the following issues (resolved in 7.1.3) needs to be applied in 7.6.x:

#99766   - Edit UI does not scale well for several sites

#111893 - Focusing the dynamic properties dialog causes annoying scroll to top behaviour

#108838 - Tinymce causes memory leakage

And also the following patches to dojo:

- Null out references in shared closure in dojo/Stateful (https://bugs.dojotoolkit.org/ticket/17771)

- Apply the memory leak fix in aspect.js (https://github.com/dojo/dojo/commit/7060d64f826286134fd8d22b7027d8ec05e6bb91)