Replace bundled pChart with szymach/c-pchart via Composer

The old pChart 1.x code that was vendored under pchart/ is removed in
favour of the maintained szymach/c-pchart package. The graph helper is

Replace bundled pChart with szymach/c-pchart via Composer

The old pChart 1.x code that was vendored under pchart/ is removed in
favour of the maintained szymach/c-pchart package. The graph helper is
rewritten to the CpChart API and no longer requires the library files
manually; DokuWiki autoloads the plugin's vendor dir. Bundled fonts come
from the package, so DroidSans.ttf is dropped too.

show more ...