Add luacheck, update translations, replace ABMs, bug fixes

[Niklp09]

copied from pyrollo#53

• 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 pyrollo/display_modpack#51
• Fixed Placing direction sign against specific nodes crashes server pyrollo/display_modpack#48
• Fixed The block signs:wooden_right_sign doesn't let a player walk through it, while signs:wooden_left_sign lets them. pyrollo/display_modpack#45
• Fixed black or green board in itemframe is shown BEHIND that itemframe, instead of in front. pyrollo/display_modpack#47 (Note: needs a very up to-date itemframes version https://notabug.org/TenPlus1/itemframes/commit/9f17f744d75a6c70f84308f66cc8c0837b550dd1)
• Fixed some other nil crashes
• Fixed digital clocks nodeboxes and textures

[wsor4035]

single thought. probably should test the code with the amount of changes