[BUGFIX] CurlEngine tries to rewind stream

This fixes an issue with the CurlEngine which executes a
rewind() on spec if the given request content is a stream
resource. This is not necessary and is especially harmful
if a stream resource is provided which does not support
seek operations.

Change-Id: I4b4629737540cf106a23ac554d58c2b459d2a1c3
Resolves: #50636
Releases: 2.0, master
[FEATURE] Allow arbitrary request methods in HTTP\Request

This patch removes a check in the HTTP Request class which
previously disallowed custom HTTP request methods such as "COPY".

Change-Id: I7a6694a71b739aba93e86d0c00c09c6eeedaf09f
Releases: master
Resolves: #50637
[WIP] A new resource management for Flow

Change-Id: Ia2b47b4070a2dfabf4833bf1f0f3967ba3b032a7