On using EltypeExtensions

[putianyi889]

Due to some interactions between packages, it takes multiple steps to not break things during the change.

• Add elconvert support to QuasiArrays but not remove LazyArrays.converteltype support using EltypeExtensions: elconvert #105
• Shift LazyArrays to elconvert using EltypeExtensions: elconvert JuliaArrays/LazyArrays.jl#290
• Remove LazyArrays.converteltype support from QuasiArrays
• Remove converteltype from LazyArrays