sysctl script check, bug fix, ply export

[rosejn]

I just wanted to share some minor tweaks and improvements I've made while studying and experimenting with your codebase. Thanks for sharing! Such a help for the research community, and for education.

• added some conditionals around sudo sysctl calls in bash script so sudo isn't required once socket buf limits have been changed
• fixed a bug in the post optimization script which made it crash before any training, now it works
• added a ply file export script which takes in your config file path like the other scripts and produces a ply file that works with various splat renderers on the intertubes.

[Nik-V9]

Thanks for this pull request! It has been merged in: https://github.com/spla-tam/SplaTAM/pull/78