* fix(test): add testcase for write integer values
* fix(lwm2m): write incorrect integer to device
* fix(emqx_lwm2m): refactor the code for getting bits len of a signed int
* chore(emqx_lwm2m): bump version for emqx_lwm2m to 4.3.3
And move emqx app back to root level
After realising the challenges of developing plugins in standalone
rebar projects. it is perhaps more smooth to keep using emqx as
a rebar dependency
Shawn