If you made a backup, then you can get them back by loading the backup. If not, rest in piece items.
Do not, and I mean DO NOT! downgrade from 1.8
Item's are saved completely differently in 1.8 than they are in 1.7. A simple way to explain it:
All the items in his chests/inventory are saved in memory where it can be accessed later, by opening the chest or inventory. They started saving in 1.8 in a way that was faster, but luckily 1.8 came with instructions on how to convert 1.7 items to 1.8 items. When you downgrade to 1.7, the game says "What is all this! I dont know how to handle this type of save information!" and just throws them out.
Intended. You must have seen YouTubers have glass do this, they are using a modded client called "OptiFine" that has preformance boosts and a option to make "connected textures" which is what you are not seeing.
You should only report one issue at a time. In the top left of the crash report, there is a button that says "report to mojang".
Intended.
If the bug is that you cannot start minecraft, then you should give a summary and description that says so. You need a summary that says what the bug is, and a description that gives clear instructions on what you expected, what actually happened, and the steps to reproduce. Here is an example of the correct formatting and report: https://bugs.mojang.com/browse/MC-1
arrg, i did a search!
Snapshots are VERY laggy, especially with max settings. Make there be fast graphics, minimal particles, etc until you make Minecraft look as bad as possible, then it should work fine. Another reason for this is the possibility of you using Optifine for Minecraft 1.7.9. This increases your frames so much that it seems odd when you cant use it.
You are in Peaceful Mode.
I think the main reason for this happening is the mouse going off of minecraft. This is one of the many reasons everyone plays in fullscreen mode.
Well, now you know! Make sure you have at least 1 backup up every world you care about!