dev-util/idea-community: bump to 2019.1 and Split custom-jdk useflag

dev-util/idea-community: bump to 2019.1 and Split custom-jdk useflag

Upstream now offers a Java 11 based Jetbrains Runtime,
while continuing to offer their Java 8 based runtime as the default download

Closes: https://bugs.gentoo.org/653144
Closes: https://bugs.gentoo.org/676370
Closes: https://bugs.gentoo.org/676900
Closes: https://bugs.gentoo.org/640688
Package-Manager: Portage-2.3.62, Repoman-2.3.12
Signed-off-by: Kyle Elbert <kcelbert@gmail.com>
Signed-off-by: Alice Ferrazzi <alicef@gentoo.org>