That is in the works, multiplayer and easy portal downloads first though 
The plugin modifications and 7zip-cpp are MIT, SevenZip++ is public domain.
7-Zip is LGPL + UnRar restriction which simply means you can’t compress RAR or make a RAR archiver (this plugin won’t allow you to compress RAR anyway, just decompress), decompressing/unarchiving is allowed and you just need to retain that specific notice in your license
- The unRAR sources cannot be used to re-create the RAR compression algorithm,
which is proprietary. Distribution of modified unRAR sources in separate form
or as a part of other software is permitted, provided that it is clearly
stated in the documentation and source comments that the code may
not be used to develop a RAR (WinRAR) compatible archiver.*
You can comment one line of code to remove the Unrar restriction using 7za.dll instead of 7z.dll by changing line 138 and 139 in ZipFileFunctionLibrary, this will however limit your archive support to .7z only due to how 7za.dll is compiled (you can in theory re-enable everything but RAR, but you will need to recompile a compatible 7zip dll yourself using the LZMA sdk which is public domain), for my own purposes the unrar restriction is acceptable and I prefer the wider archive support so I default to 7z.dll.
Regarding LGPL, because this plugin is using the com-like port interface to the 7zip .dll it doesn’t cause the rest of the code (e.g. modifications and any unrelated code) to fall under LGPL. From the wiki on LGPL: a standalone executable that dynamically links to a library through a .so, .dll, or similar medium is generally accepted as not being a derivative work as defined by the LGPL. It would fall under the definition of a “work that uses the Library”.
Paragraph 5 of the LGPL version 2.1 states: A program that contains no derivative of any portion of the Library, but is designed to work with the Library by being compiled or linked with it, is called a “work that uses the Library”. Such a work, in isolation, is not a derivative work of the Library, and therefore falls outside the scope of this License.
While not relevant, that dll barrier is actually another static library (7zip-cpp) away from the plugin in release mode and another dynamic link barrier in editor mode (this plugin .dll).
TL;DR:
It may be not trivial to parse but you are ok with using this plugin commercially with the license file included, that said I’m not a lawyer and you should make your own judgement, refer to the plugin license file for details.