Provide mappings or deobfuscation for old versions to easier modding

Many people continue playing old Java releases, such as 1.12.2, 1.7.10, 1.6.4, b1.7.3, etc. The reasons are diverse. Some people have no access to the modern hardware; others just refuse to play new versions due to content they provide. 

Complete mappings or deobfuscation will make those versions even more accessible than before. Moreover, the community will most likely handle the majority of problems related to launching these versions on modern hardware by themselves by modding them.