To allow us to refactor some common operations that we use in our recipes that depends on android's STL library.

Note: This commit will allow us to begin the migration to `c++_shared`. This is a must when we move to android's NDK r19+, because as for android NDK >= 18 is the only one supported STL library.

…support

Also done here:
  - Remove hardcoded version in url
  - Disable versioned shared libraries
  - Make it to be build as a shared libraries (instead of static)
  - Disable the build of static libraries (because we build them as shared ones, so we avoid to link with them without our consents)
  - Shorten long lines to be pep8's friendly
  - Remove icu from ci/constants
  - Remove `RuntimeError` about the need to use NDK api <= 19 (because that is not the case anymore)
  - consider host's number of cpu to perform the build

Also done here:
  - Remove icu.patch because now we don't have the version in our icu libraries
  - Shorten long lines to be pep8's friendly

make it work with the reworked snappy recipe

which:
  - fix build for android's NDK r19+
  - allow us to build `boost+libtorrent` for any arch
  - Update boost to version `1.69.0`
  - update libtorrent to version `1.2.1`

The build method needs to be changed because one of the scripts used in `boost+libtorrent` build (make-standalone-toolchain.sh), has been removed from android's NDK. [This is because](https://developer.android.com/ndk/guides/standalone_toolchain):

`As of r19, the NDK's default toolchains are standalone toolchains, which renders this process unnecessary.`

Note: since 3887d2b, `python-for-android` uses android's NDK r19 as the minimum supported and also changed the build method used by p4a as [described in here](https://developer.android.com/ndk/guides/other_build_systems)

In here we do:
  - inherit from CppCompiledComponentsPythonRecipe Because depends on android's STL library
  - make use of the base class methods for library recipes
  - Split build_arch into proper methods
  - Shorten some long lines (to be PEP8 friendly)
  - make generated library shared
  - remove recipe from CI/constants