New flag BC_Resources::locale_utf8

Indicates that utf8 encoding is in use.
Set on base of the locale information
Using BC_Resources::locale_utf8 for text output
New function BC_WindowBase::draw_utf8_text

Intended usage: printing literal constants with known encoding
Using BC_WindowBase::draw_utf8_text for Credits

Names in credits are not translated - they are always in known encoding.
Use xft font parameters to get the height of row
Moved intput context creation to BC_WindowBase::init_im

Input context is created for main window and destoyed when
window is closed. Flag BC_Resources::missing_im notes failed
intput context creation.
Fix utf8 input and make non-utf8 input work

Simplified and unified keypress conversion path
Fixed handling of delete key with utf8

The length of next symbol is required
Fix calculating of string length for non-utf8 locale

All symbols of non-utf8 codetables are 1 byte
New icon of unsharp plugin

The old icon was too political