[i18n] fix ts and qm file generation - JB#18560 & JB#18561

1) The *.ts files in the project source directory are updated by
lupdate, then copied to the project output directory.

2) lrelease reads the *.ts files in the output directory and creates
*.qm files from them.

3) Steps 1 and 2 take place in 'make install' phase.

This all works in shadow build and in-srctree build mode and with
a project path which has some white space.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
Merge pull request #10 from sailfish-sdk/jb18561

[i18n] Fix shadow builds. Fixes JB#18560
[i18n] Only run i18n build during "make install". Fixes JB#18561