Translation updates and maintenance

[Niklp09]

@pyrollo

• Replaced ontime_clocks ABMs w/ nodetimers
• Removed intllib support + po files [and .po tools]
• Removed 0.4 compatibility code
• Added mt 5 tranlation support + new templates
• Added German translation
• Added translation support to font formspec
• Added luacheck + fixed luacheck warnings
• Fixed punching a blackboard/greenboard changes the formspec #51
• Fixed Placing direction sign against specific nodes crashes server #48
• Fixed The block signs:wooden_right_sign doesn't let a player walk through it, while signs:wooden_left_sign lets them. #45
• Fixed black or green board in itemframe is shown BEHIND that itemframe, instead of in front. #47 (Note: needs a very up to-date itemframes version https://notabug.org/TenPlus1/itemframes/commit/9f17f744d75a6c70f84308f66cc8c0837b550dd1)
• Fixed some other nil crashes

[Niklp09]

Replaced by mt-mods#1. Replying to emails or github notifications would be very helpful...