Various fixes, cleanup, performance improvements, QoL

[Birdy2014]

This PR is a disjointed mess of multiple fixes, performance improvements and style changes. It does way too much for one PR, however, I originally just wanted to bundle some very small changes, and it kind of escalated.

Scene save files from the main branch are not compatible and will result in a broken scene.

Memory / Performance:

• Fixes a memory leak -> lowers the memory consumption from ~500 MB to ~270MB.
• Adds a shader uniform location cache, removes unnecessary VAO bind calls and merges meshes when possible -> Lowers the per core CPU usage on my machine from around 200% to 160% when running with 120 fps.
• Fixes the AssetBrowser model preview always being recomputed
• Adds a "Performance" window (visible in debug mode only) that shows frametime, fps, background threadpool utilization, amount of loaded textures and models

QoL:

• Moves the Nodes and vertices in such a way that the gizmos are always displayed in the center of object. Previously, the gizmos where shown far away of some buildings. This changes object positions, so we might want to add an option to disable this feature later.
• Allows the deletion of objects by pressing the delete key while the viewport is focused
• Show gizmo keybindings in gizmo operation dropdown
• Adjusts default speed and scale gizmo snap values

Other stuff:

• Adds compatibility with gcc
• Renames Texture::m_id to Texture::id. Only private members should be prefixed with m_ and this is just the instance that I really noticed. However there are more occurrences I didn't fix. Maybe I should not bother and remove the commit?
• Fixes outlines breaking sometimes when switching between albedo and rendered shading mode
• Fixes not in ObjectSelectionTree not remembering whether they are opened or not if a node is moved before it or if a previous node is deleted

[LazyBone2017]

Debug Window Works
Gizmos are placed correctly
Increased defaults are there
keybinds are visible
deletion of mouse picked object works
memory usage ~270MB