getExtensions() {
        this.extensions = [];
        if(this._isWebGL2) {
            this.extensions['EXT_color_buffer_float'] = this.gl.getExtension('EXT_color_buffer_float');
            this.extensions['OES_texture_float_linear'] = this.gl.getExtension('OES_texture_float_linear');
            this.extensions['EXT_texture_filter_anisotropic'] = this.gl.getExtension('EXT_texture_filter_anisotropic');
            this.extensions['WEBGL_lose_context'] = this.gl.getExtension('WEBGL_lose_context');
        } else {
            this.extensions['OES_vertex_array_object'] = this.gl.getExtension('OES_vertex_array_object');
            this.extensions['OES_texture_float'] = this.gl.getExtension('OES_texture_float');
            this.extensions['OES_texture_float_linear'] = this.gl.getExtension('OES_texture_float_linear');
            this.extensions['OES_texture_half_float'] = this.gl.getExtension('OES_texture_half_float');
            this.extensions['OES_texture_half_float_linear'] = this.gl.getExtension('OES_texture_half_float_linear');
            this.extensions['EXT_texture_filter_anisotropic'] = this.gl.getExtension('EXT_texture_filter_anisotropic');
            this.extensions['OES_element_index_uint'] = this.gl.getExtension('OES_element_index_uint');
            this.extensions['OES_standard_derivatives'] = this.gl.getExtension('OES_standard_derivatives');
            this.extensions['EXT_sRGB'] = this.gl.getExtension('EXT_sRGB');
            this.extensions['WEBGL_depth_texture'] = this.gl.getExtension('WEBGL_depth_texture');
            this.extensions['WEBGL_draw_buffers'] = this.gl.getExtension('WEBGL_draw_buffers');
            this.extensions['WEBGL_lose_context'] = this.gl.getExtension('WEBGL_lose_context');
        }
    }
Get all available WebGL extensions based on WebGL used version
     Called on init and on context restoration
*