apply formstyle for login form (bootstrap not supported yet)

removed the additional formstyle setting, now using an inline-parameter to switch formstyles however this switch depends on the _inline suffix of the formstyle name which i think is more fragile than a separate deployment setting, and then there is no formstyle_bootstrap_inline so it's not applicable for that

apart from that, bootstrap custom styles for the default login form are fairly spread out, likewise the custom hacks to bend the default formstyle to look like bootstrap (the latter check for bootstrap setting but expect default formstyle), and then there are various custom CSS overrides for bootstrap forms which prevent the formstyle from being applicable for embedded login forms (including some pixel-wise positioning without obvious reason), and all that appears to be implemented jenga-style so that it can not easily be corrected without breaking everything else in the various bootstrap themes

suggest a step-by-step approach:
a) leave the bootstrap workaround in place for now
b) make it overridable (temporary switch), then fix theme by theme, issue by issue
c) once completely fixed, remove the override switch and the bootstrap workaround

after taking a closer look, i wonder whether bootstrap-formstyle for login forms is at all desired?